C parser/preprocessing

[saidctb]

Summary

Adds the first C parser Phase 4 foundation for raw source handling and metadata extraction.

This PR introduces:

• C lexer/source normalization helpers
• safe // and /* ... */ comment stripping while preserving line/column accounting
• string and character literal awareness during comment stripping
• backslash-newline logical record folding
• lightweight C tokens with source locations
• raw #include collection for quoted and system includes
• local include resolution relative to the parsed file
• simple object-like #define macro collection
• function-like macro metadata plus non-fatal unsupported diagnostics
• parser/API wiring so parse_c_file populates raw includes, macros, and metadata diagnostics
• CLI JSON coverage for the new C metadata output
• updated C parser docs/checklist for implemented behavior and future macro policy

Declaration, function, struct, typedef, and project-resolution parsing remain intentionally deferred.

C Macro And Preprocessing Policy

Clarifies that the C parser is preprocessor-aware, not a C preprocessor:

• raw C mode only normalizes source and records directive metadata
• raw mode parses only declarations already visible as ordinary C
• raw mode must not expand macros, select #if/#ifdef branches, or treat macro-generated declarations as parsed API
• macro-heavy APIs require future compiler-preprocessed input
• preprocessed input must preserve #line/linemarker mapping so diagnostics and source_location fields point back to the original .h/.c

Tests

• python3 -m pytest -q tests/parser/c/test_c_public_api_skeleton.py tests/parser/c/test_c_lexer_preprocessor.py tests/parser/c/test_c_cli_skeleton.py
• python3 -m pytest -q
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 96.59864% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
c_parser/preprocessor.py	91.52%	2 Missing and 3 partials ⚠️

Flag	Coverage Δ
py312	92.56% <96.59%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
c_parser/lexer.py	100.00% <100.00%> (ø)
c_parser/parser.py	90.83% <ø> (ø)
c_parser/preprocessor.py	91.52% <91.52%> (+91.52%)	⬆️

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