Preserve CRLF boundaries when deleting comments - #3135

Summary

Rewriter#delete_comment currently assumes every comment line ends with exactly one byte. That removes LF correctly, but removes only the carriage return from CRLF input and leaves a blank LF line behind. It can also extend one byte past a comment at EOF.

This change advances over the actual optional carriage-return and newline bytes instead of adding one unconditionally.

Verification

• external LF, CRLF, and comment-at-EOF boundary models
• Rewriter tests: 20/20
• RDoc annotator tests: 10 tests / 13 assertions
• complete signature validation and native extension compilation
• release-based gem build/install: 568 files; native parser, schemas, and rewrite behavior pass

The behavior for ordinary LF comments remains unchanged.