Add CPython C PEG parser to benchmark comparison (4th parser)

Benchmark CPython's internal PEG parser at the mod_ty (C struct) level,
calling _PyPegen_run_parser_from_string() directly without Python AST
object creation. CPython is 6.45x slower than Ruff (4,648ms vs 721ms).

All 12 plots regenerated with 4 parsers. Report updated with CPython
architectural analysis (PEG memoization overhead, generated parser
dispatch, arena allocation) and updated recommendations.

https://claude.ai/code/session_0116H8dSsjY7pmMiZs5WWjF3

Author: claude