Refactor Rust parser to use Tree-sitter queries and improve formatters (done by jules in 24m)

[tyrchen]

This commit introduces several enhancements to the Rust parsing and formatting capabilities:

1. Rust Parser Refactoring (src/parser/lang/rust.rs):

   • The Rust parser now extensively uses Tree-sitter queries for identifying and extracting code elements (functions, structs, enums, traits, impls, modules, attributes, visibility modifiers, documentation). This replaces much of the previous manual AST node traversal logic.
   • Item-specific queries (FUNCTION_QUERY, STRUCT_QUERY, etc.) have been defined and integrated.
   • A hybrid approach is used for attributes and visibility, combining query captures with existing helper functions to correctly handle both preceding and direct child elements.
   • Documentation parsing continues to primarily use the extract_documentation helper, which identifies specific Rust doc comment patterns.

2. Enhanced Parser Unit Tests (src/parser/lang/rust.rs):

   • The existing parser test suite has been verified and significantly expanded.
   • New fixture files (fixtures/sample_advanced.rs, fixtures/empty.rs, fixtures/only_comments.rs) were added.
   • fixtures/sample.rs was heavily updated.
   • New tests cover a wider range of scenarios, including complex generics, various attribute and documentation styles, different visibility modifiers (including pub(in path)), nested items, extern crate, use declarations, mod declarations, and edge cases like empty or comment-only files.
   • Assertions have been made more granular.

3. Formatter Refinements (src/parser/formatter/mod.rs):

   • TraitUnit formatting for Summary and NoTests strategies now uses a more accurate head string (derived from self.source or self.head if it were present).
   • The Summary strategy for StructUnit now correctly handles commas for fields, preventing double commas.
   • Minor output trimming for cleaner formatting of files and modules.

4. New Formatter Unit Tests (src/parser/formatter/rust.rs):

   • A new test file dedicated to Rust formatters has been added.
   • Tests include end-to-end scenarios (parsing fixture files then formatting the FileUnit) for all strategies.
   • Specific tests verify the formatter refinements for TraitUnit heads and StructUnit field commas.
   • Coverage includes various Rust constructs and formatting strategies.

Note on Testing:
Due to a build environment issue preventing cargo test execution, all test creation, updates, and verification were performed through manual code review and analysis of expected behavior.