fix(core): encode reserved path chars in file URIs

[dergachoff]

Summary

Fixes #150.

path_to_uri formatted file URIs as file://{path}. Valid filesystem paths containing URI-reserved characters, such as bracketed route filenames, produced invalid raw URI paths. lsp_types::Uri::from_str then returned UnexpectedChar; because this path used expect, diagnostics requests could panic and abort the MCP stdio server.

This builds platform-aware file URLs with Url::from_file_path, preserves the existing Windows-rooted synthetic test-path behavior, encodes RFC3986-invalid path characters that WHATWG URL leaves raw in the path ([, ], ^, |), and adds a regression test for a route-style filename with uri_to_path round-trip coverage.

Validation

• cargo +nightly fmt --check
• cargo +1.95 test -p mcpls-core path_to_uri
• cargo +1.95 test -p mcpls-core
• cargo +1.95 clippy -p mcpls-core --all-targets --all-features -- -D warnings
• rustup target add --toolchain 1.95 x86_64-pc-windows-msvc && cargo +1.95 check -p mcpls-core --target x86_64-pc-windows-msvc --all-targets --all-features
• Manual MCP stdio probe: before the patch, get_diagnostics on a bracketed route path aborted with failed to create URI from path: ParseError { ... UnexpectedChar }; after the patch, the same call returned a normal tool response.