Two fixes:
1. Hex string lexer now flushes dangling nibble when encountering invalid
characters. For `<4X8Y>`, the X and Y are invalid, so we flush nibble 4
as 0x40, then flush nibble 8 as 0x80, producing `\x40\x80`.
2. Fixed skip_whitespace_and_comments() to properly handle whitespace
after comments. The previous logic only continued looping if the next
byte was `%`, missing cases where whitespace follows a comment.
All 52 lexer tests pass.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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