fix: update unlaxer to 3.0.15 and remove mapper reflection

[opaopa6969]

Closes #98

Summary

• update unlaxer-common and unlaxer-dsl to 3.0.15
• use generated Mapper.mapParsedToken for existing token trees
• use public StringSource.createRootSource and Token.getToken APIs
• remove the 3.0.14 block-comment source rewrite workaround

Validation

• git diff --check passes
• local Maven compile could not run because this environment has no Java runtime; GitHub CI should validate generation and parity tests.

The 3.0.15 generator contains the requested public mapping API and corrected javaStyle block-comment handling. No handwritten-backend fallback was added.