peg-parser: rename preserved() to token(), resolve token IDs at runtime
- Rename common_peg_preserved_parser to common_peg_token_parser
- Rename preserved() method to token() for cleaner API
- Token IDs are now resolved at parse time from context's token_ids map
instead of being hardcoded in the parser definition
- Add token_ids map to common_peg_parse_context for runtime resolution
- Update FunctionGemma parser to use new token() API
- Wire up FunctionGemma PEG parser (COMMON_CHAT_FORMAT_PEG_FUNCTION_GEMMA)
- Update all tests to use new token() method and provide token_ids map
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>