feature: codeblocks should have a true left margin

从插件的代码配置入手，尤其是现有的 left_margin、left_pad、background_inset 和 width 选项，并比较标题缩进的呈现方式。完成标准是：代码块可以通过可配置的边距向右移动，同时背景覆盖该边距而不影响缩进线。

Is your feature request related to a problem? Please describe.

margin for other elements like headings, bullets etc is true margin i.e. the cursor cannot enter that area in normal mode. codeblocks should also have a similar margin, this would improve their appearance a lot.

something like this. i have added 2 spaces before ach line of code, but that doesn't work well as the indentation lines show up on the left side. the actual codeblock markers start from that indentation line..

but if instead we can move the entire codeblock right by 2 spaces and highlight those two spaces with code block color, it would improve the appearance of the code block and also not mess up with the indentation lines.

Describe the solution you'd like

the solution would be to add an option "block_margin" or something similar which would work similar to heading indentations but the codeblock will still be rendered (the background) on those margin spaces...

Describe alternatives you've considered

alternative is to just be happy in what you have :)

Additional information

my plugin config

return {
  "MeanderingProgrammer/render-markdown.nvim",
  config = function()
    require("render-markdown").setup({
      render_modes = true,
      anti_conceal = {
        enabled = true,
        disabled_modes = false,
        above = 0,
        below = 0,
        ignore = {
          code_background = true,
          indent = true,
          sign = true,
          virtual_lines = true,
        },
      },
      link = {
        enabled = true,
        render_modes = false,
        footnote = {
          enabled = true,
          icon = "󰯔 ",
          body = function(ctx)
            return ctx.text
          end,
          superscript = true,
          prefix = "",
          suffix = "",
        },
        image = "󰥶 ",
        image_custom = true,
        email = "󰀓 ",
        hyperlink = "󰌹 ",
        highlight = "RenderMarkdownLink",
        highlight_title = "RenderMarkdownLinkTitle",
        wiki = {
          enabled = true,
          icon = "󱗖 ",
          conceal_destination = true,
          body = function()
            return nil
          end,
          highlight = "RenderMarkdownWikiLink",
          scope_highlight = nil,
        },
        custom = {
          web = { icon = "󰖟 ", pattern = "^http" },
          apple = { icon = " ", pattern = "apple%.com", kind = "url" },
          discord = { icon = "󰙯 ", pattern = "discord%.com", kind = "url" },
          github = { icon = "󰊤 ", pattern = "github%.com", kind = "url" },
          gitlab = { icon = "󰮠 ", pattern = "gitlab%.com", kind = "url" },
          google = { icon = "󰊭 ", pattern = "google%.com", kind = "url" },
          hackernews = { icon = " ", pattern = "ycombinator%.com", kind = "url" },
          linkedin = { icon = "󰌻 ", pattern = "linkedin%.com", kind = "url" },
          microsoft = { icon = " ", pattern = "microsoft%.com", kind = "url" },
          neovim = { icon = " ", pattern = "neovim%.io", kind = "url" },
          reddit = { icon = "󰑍 ", pattern = "reddit%.com", kind = "url" },
          slack = { icon = "󰒱 ", pattern = "slack%.com", kind = "url" },
          stackoverflow = { icon = "󰓌 ", pattern = "stackoverflow%.com", kind = "url" },
          steam = { icon = " ", pattern = "steampowered%.com", kind = "url" },
          twitter = { icon = " ", pattern = "twitter%.com", kind = "url" },
          wikipedia = { icon = "󰖬 ", pattern = "wikipedia%.org", kind = "url" },
          x = { icon = " ", pattern = "x%.com", kind = "url" },
          youtube = { icon = "󰗃 ", pattern = "youtube[^.]*%.com", kind = "url" },
          youtube_short = { icon = "󰗃 ", pattern = "youtu%.be", kind = "url" },
        },
      },
      bullet = {
        enabled = true,
        render_modes = false,
        icons = { "•", "•", "•", "•" },
        ordered_icons = function(ctx)
          local value = vim.trim(ctx.value)
          local index = tonumber(value:sub(1, #value - 1))
          return ("%d."):format(index > 1 and index or ctx.index)
        end,
        left_pad = 0,
        right_pad = 0,
        highlight = "RenderMarkdownBullet",
        scope_highlight = {},
        scope_priority = nil,
      },
      quote = {
        enabled = true,
        render_modes = false,
        icon = "▋",
        repeat_linebreak = false,
        highlight = {
          "RenderMarkdownQuote1",
          "RenderMarkdownQuote2",
          "RenderMarkdownQuote3",
          "RenderMarkdownQuote4",
          "RenderMarkdownQuote5",
          "RenderMarkdownQuote6",
        },
      },
      callout = {
        note = {
          raw = "[!NOTE]",
          rendered = "󰋽  Note",
          highlight = "RenderMarkdownInfo",
          category = "github",
        },
        tip = {
          raw = "[!TIP]",
          rendered = "󰌶 Tip",
          highlight = "RenderMarkdownSuccess",
          category = "github",
        },
        important = {
          raw = "[!IMPORTANT]",
          rendered = "󰅾  Important",
          highlight = "RenderMarkdownHint",
          category = "github",
        },
        warning = {
          raw = "[!WARNING]",
          rendered = "󰀪  Warning",
          highlight = "RenderMarkdownWarn",
          category = "github",
        },
        caution = {
          raw = "[!CAUTION]",
          rendered = "󰳦  Caution",
          highlight = "RenderMarkdownError",
          category = "github",
        },
        abstract = {
          raw = "[!ABSTRACT]",
          rendered = "󰨸  Abstract",
          highlight = "RenderMarkdownInfo",
          category = "obsidian",
        },
        summary = {
          raw = "[!SUMMARY]",
          rendered = "󰨸  Summary",
          highlight = "RenderMarkdownInfo",
          category = "obsidian",
        },
        tldr = {
          raw = "[!TLDR]",
          rendered = "󰨸  TL;DR",
          highlight = "RenderMarkdownInfo",
          category = "obsidian",
        },
        info = {
          raw = "[!INFO]",
          rendered = "󰋽  Info",
          highlight = "RenderMarkdownInfo",
          category = "obsidian",
        },
        todo = {
          raw = "[!TODO]",
          rendered = "󰗡  Todo",
          highlight = "RenderMarkdownInfo",
          category = "obsidian",
        },
        hint = {
          raw = "[!HINT]",
          rendered = "󰌶 Hint",
          highlight = "RenderMarkdownSuccess",
          category = "obsidian",
        },
        success = {
          raw = "[!SUCCESS]",
          rendered = "󰄬  Success",
          highlight = "RenderMarkdownSuccess",
          category = "obsidian",
        },
        check = {
          raw = "[!CHECK]",
          rendered = "󰄬  Check",
          highlight = "RenderMarkdownSuccess",
          category = "obsidian",
        },
        done = {
          raw = "[!DONE]",
          rendered = "󰄬  Done",
          highlight = "RenderMarkdownSuccess",
          category = "obsidian",
        },
        question = {
          raw = "[!QUESTION]",
          rendered = "󰘥  Question",
          highlight = "RenderMarkdownWarn",
          category = "obsidian",
        },
        help = {
          raw = "[!HELP]",
          rendered = "󰘥  Help",
          highlight = "RenderMarkdownWarn",
          category = "obsidian",
        },
        faq = {
          raw = "[!FAQ]",
          rendered = "󰘥  Faq",
          highlight = "RenderMarkdownWarn",
          category = "obsidian",
        },
        attention = {
          raw = "[!ATTENTION]",
          rendered = "󰀪  Attention",
          highlight = "RenderMarkdownWarn",
          category = "obsidian",
        },
        failure = {
          raw = "[!FAILURE]",
          rendered = "󰅖 Failure",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        fail = {
          raw = "[!FAIL]",
          rendered = "󰅖 Fail",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        missing = {
          raw = "[!MISSING]",
          rendered = "󰅖 Missing",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        danger = {
          raw = "[!DANGER]",
          rendered = "󱐌 Danger",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        error = {
          raw = "[!ERROR]",
          rendered = "󱐌 Error",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        bug = {
          raw = "[!BUG]",
          rendered = "󰨰 Bug",
          highlight = "RenderMarkdownError",
          category = "obsidian",
        },
        example = {
          raw = "[!EXAMPLE]",
          rendered = "󰉹  Example",
          highlight = "RenderMarkdownHint",
          category = "obsidian",
        },
        quote = {
          raw = "[!QUOTE]",
          rendered = "󱆨  Quote",
          highlight = "RenderMarkdownQuote",
          category = "obsidian",
        },
        cite = {
          raw = "[!CITE]",
          rendered = "󱆨  Cite",
          highlight = "RenderMarkdownQuote",
          category = "obsidian",
        },
      },
      checkbox = {
        enabled = false,
        render_modes = false,
        bullet = false,
        left_pad = 0,
        right_pad = 1,
        unchecked = {
          icon = "󰄱 ",
          highlight = "RenderMarkdownUnchecked",
          scope_highlight = nil,
        },
        checked = {
          icon = "󰱒 ",
          highlight = "RenderMarkdownChecked",
          scope_highlight = nil,
        },
        custom = {
          todo = { raw = "[-]", rendered = "󰥔 ", highlight = "RenderMarkdownTodo", scope_highlight = nil },
        },
        scope_priority = nil,
      },
      code = {
        enabled = true,
        render_modes = true,
        sign = false,
        conceal_delimiters = false,
        language = true,
        position = "left",
        language_icon = false,
        language_name = false,
        language_info = false,
        language_pad = 0,
        disable = {},
        disable_background = { "diff" },
        background_inset = 1,
        width = "block",
        left_margin = 0,
        left_pad = 0,
        right_pad = 0,
        min_width = 90,
        border = "thin",
        language_border = "█",
        language_left = "",
        language_right = "",
        above = "▄",
        below = "▀",
        inline = true,
        inline_left = "",
        inline_right = "",
        inline_pad = 0,
        priority = 140,
        highlight = "RenderMarkdownCode",
        highlight_info = "RenderMarkdownCodeInfo",
        highlight_language = nil,
        highlight_border = "RenderMarkdownCodeBorder",
        highlight_fallback = "RenderMarkdownCodeFallback",
        highlight_inline = "RenderMarkdownCodeInline",
        highlight_inline_left = nil,
        highlight_inline_right = nil,
        style = "full",
      },
      dash = {
        enabled = true,
        render_modes = false,
        icon = "─",
        width = "full",
        left_margin = 0,
        priority = nil,
        highlight = "RenderMarkdownDash",
      },
      indent = {
        enabled = true,
        render_modes = true,
        per_level = 1,
        skip_level = 1,
        skip_heading = false,
        icon = " ",
        priority = 0,
        highlight = "RenderMarkdownIndent",
      },
      paragraph = {
        enabled = true,
        render_modes = false,
        left_margin = 0,
        indent = 0,
        min_width = 0,
      },
      heading = {
        enabled = true,
        render_modes = false,
        atx = true,
        setext = true,
        sign = false,
        -- icons = { "◉  ", "○  ", "✸  ", "✿  ", "✿  ", "✿  " },
        icons = { "# ", "## ", "### ", "#### ", "##### ", "###### " },
        position = "overlay",
        signs = { "󰫎 " },
        width = "full",
        left_margin = 0,
        left_pad = 0,
        right_pad = 0,
        min_width = 0,
        border = false,
        border_virtual = false,
        border_prefix = false,
        above = "▄",
        below = "▀",
        backgrounds = {
          "RenderMarkdownH1Bg",
          "RenderMarkdownH2Bg",
          "RenderMarkdownH3Bg",
          "RenderMarkdownH4Bg",
          "RenderMarkdownH5Bg",
          "RenderMarkdownH6Bg",
        },
        foregrounds = {
          "RenderMarkdownH1",
          "RenderMarkdownH2",
          "RenderMarkdownH3",
          "RenderMarkdownH4",
          "RenderMarkdownH5",
          "RenderMarkdownH6",
        },
        custom = {},
      },
      pipe_table = {
        enabled = true,
        render_modes = true,
        preset = "none",
        cell = "padded",
        cell_offset = function()
          return 0
        end,
        padding = 1,
        min_width = 0,
        border = {
          "┌",
          "┬",
          "┐",
          "├",
          "┼",
          "┤",
          "└",
          "┴",
          "┘",
          "│",
          "─",
        },
        border_enabled = false,
        border_virtual = false,
        alignment_indicator = "━",
        head = "RenderMarkdownTableHead",
        row = "RenderMarkdownTableRow",
        style = "full",
      },
      completions = {
        lsp = { enabled = true },
      },
    })
  end,
}