fix(lsp): respect .stylua.toml on Windows file URIs

[SergioChan]

Summary

• normalize LSP file URIs into filesystem paths before config and ignore resolution
• strip the leading slash from Windows drive-letter paths (/C:/... -> C:/...) so .stylua.toml lookup works in --lsp mode
• add URI-to-path regression tests (cfg-gated for unix/windows)

Testing

• git diff --check
• Could not run Rust tests in this environment because cargo is not installed (/bin/bash: cargo: command not found)

Related

Fixes #1051

[JohnnyMorganz]

Please do not open PRs if your automated system fails to verify the changes locally first, because it cannot access cargo. #1078 is already failing.