fix: consume whitespace after hexadecimal escapes

[jakezwang]

Parsing [x="\000061 b"] currently produces the attribute value a b instead of ab. Changing the node's quote mark then serializes a selector matching a different value.

Consume the optional CSS whitespace after the hexadecimal digits, including after a six-digit escape. Handle CRLF as one newline and preserve the original raw selector. Add public parser regressions for each whitespace form, replacement characters, and boundaries that must stay in the value.

Validation: 15 regression cases fail before the fix. npm test passes lint, types, coverage thresholds, and all 834 tests on Node 24 and 26. The existing 30 unescape tests also pass; 48 original/reserialized selector pairs match the expected attribute in Chrome. Changed-file formatting passes; the full formatting check flags only unchanged src/__tests__/exceptions.mjs.