Add rust dependency

[CppCXY]

1. To achieve better extensibility and higher performance, introduce Rust extension libraries.
2. Replace the formatter with emmylua_formatter.

[ishermandom]

Thanks for your work on this tool! I've arrived here from investigating zed-extensions/lua#56.

Using Claude, I built this PR and compared it with 3.19.1 over LSP. I found two small bugs, and I have one question:

1. The editor's tabSize and insertSpaces are ignored.

   formatting.lua passes options as the third argument, but l_format reads only two. So an editor set to 2 spaces or to tabs gets the whole file re-indented to 4 spaces.

   Potential fix: apply them over the .luafmt.toml config, as emmylua_ls does in build_workspace_formatter_config.

2. The .luafmt.toml lookup gets a file:// URI where a path is expected.

   AFAICT, currently: .luafmt.toml is looked up from the server's working directory instead of the file's folder. A config in a subfolder is never used, and the root config works only if the server was started there.

   Potential fix: pass furi.decode(uri) in script/core/formatting.lua, where it calls rust.luafmt.format.

3. Question: Whole-file formatting now ignores .editorconfig and Lua.format.defaultConfig, but range formatting still uses them. For example, with quote_style = single, only range formatting changes "x" to 'x'. Is that split intended?

Claude built a tested patch for 1 and 2, with test cases. I can post it if that helps.