Unquote and unescape Content-Type: charset [RFC7230]

从 issue 中所示的 lib/net/http/header.rb 参数解析代码开始，然后针对包含带引号 charset 的 response 运行提供的 Net::HTTP 复现。验证带引号和经过转义的 Content-Type 参数能够生成有效的 encoding 名称，并且 request 能够成功完成；如果 repository 现有的测试提供了合适的位置，则添加回归覆盖。

uri = URI('http://127.0.0.1:8080')
http = Net::HTTP.new(uri.hostname, uri.port)
http.response_body_encoding = true
http.send_request('GET', uri.request_uri)

/opt/homebrew/lib/ruby/gems/4.0.0/gems/net-http-0.9.1/lib/net/http/response.rb:381:in 'String#force_encoding': unknown encoding name - "UTF-8" (ArgumentError)
    @body.force_encoding(enc) if enc
	from /opt/homebrew/lib/ruby/gems/4.0.0/gems/net-http-0.9.1/lib/net/http/response.rb:381:in 'Net::HTTPResponse#read_body'

$ curl -I http://127.0.0.1:8080/
Content-Type: text/html; charset="UTF-8"
Server: WEBrick/1.9.2 (Ruby/4.0.1/2026-01-13)

$ open https://www.rfc-editor.org/rfc/rfc7230#section-3.2.6

[3.2.6](https://www.rfc-editor.org/rfc/rfc7230#section-3.2.6). Field Value Components
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE

$ git diff
diff --git a/lib/net/http/header.rb b/lib/net/http/header.rb
index 797a3be..fe026ae 100644
--- a/lib/net/http/header.rb
+++ b/lib/net/http/header.rb
@@ -762,3 +762,3 @@ module Net::HTTPHeader
       k, v = *param.split('=', 2)
-      result[k.strip] = v.strip
+      result[k.strip] = v.strip.gsub(/\A"(.*?)(?<!\\)"\z/) { $1.gsub(/\\(.)/, '\1') }.strip
     end

http.send_request('GET', uri.request_uri)
# #<Net::HTTPOK 200 OK readbody=true>