Mise plugin for gem tools

We want to offer a Mise backend plugin that manages tools written in Ruby via the rv tool mechanism. Mise users will be able to manage and use gem CLI tools with fully managed and isolated environments without worrying about dependency conflicts or Homebrew upgrades breaking things.

• create a backend plugin from the mise backend template at spinel-coop/mise-rv-gems
• implement tool installation and management via the rv tool subcommands, following the mise backend docs
• update the rv readme to include instructions on using rv to manage gem tools, something like:

Use rv to install and manage CLI tools written in Ruby, guaranteeing isolated environments for each tool and no mysterious errors when Homebrew automatically updates OpenSSL:

mise plugin install rv https://github.com/spinel-coop/mise-rv-gem
mise use -g rv:gist
gist -p README.md

Open questions

Is it possible to replace the built-in gem backend, so we can provide mise use gem:gist instead of mise use rv:gist?