Add TODO comments and rename use_new_parsers → experimental_new_parsers
- Add TODO comments marking legacy init/parse functions for removal
once --experimental-new-parsers feature graduates
- Also mark 1st-gen PEG format enums (PEG_SIMPLE, PEG_NATIVE, PEG_CONSTRUCTED)
- Rename use_new_parsers to experimental_new_parsers for consistency
with the CLI flag --experimental-new-parsers
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>