feat: add yieldPercentSymbols option to emit PERCENT_SYMBOL tokens

[mlightcad]

Summary

• Add new TokenType.PERCENT_SYMBOL and PercentSymbolData type for structured AutoCAD %% symbol codes
• Add yieldPercentSymbols parser option (default false) to emit symbol tokens instead of expanding into WORD characters
• Support named codes (%%c, %%d, %%p), numeric codes (%%ddd), and literal percent (%%%)
• Add comprehensive tests and bump version to 1.5.0

Test plan

• Run npm test — yieldPercentSymbols test suite passes
• Verify default behavior unchanged when yieldPercentSymbols is false or omitted
• Confirm named, numeric, and literal %% codes emit correct PERCENT_SYMBOL token data

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