The serializer's escaping functions rebuilt every text, attribute, comment,
and processing-instruction value character by character, even when the value
contained nothing to escape, which is the common case. Each now scans the
value's UTF-8 bytes for the bytes it would escape (the markup characters, the
active attribute quote, the whitespace characters, a comment hyphen, a PI
question mark, and any non-ASCII byte in ASCII-only mode) and returns the
value unchanged when none is present, taking the original character path only
when something must be escaped.
Measured serialize roughly halved, ~5.5x to ~2.7x slower than libxml2 on the
20k-item generated corpus, with byte-identical output. EscapingFastPathTests
pins both the unchanged fast path and the escaped slow path for each function,
and the Apache Xalan XSLT gold-output corpus (a serialize-heavy differential)
stays green. No output changed.
