bench: update @tuananh/sax-parser to 1.6 and txml to 6, refresh numbers

[evoactivity]

What

Updates the two comparison libraries that shipped major releases and refreshes BENCHMARKS.md with numbers against them (Node 24, same hardware as all previous published runs).

• @tuananh/sax-parser ^1.2.0 → ^1.6.0
• txml ^5.2.1 → ^6.0.0 — v6 removed the txml/dist/txml.js deep import in favour of the txml/txml export and renamed tNode → TNode, so the three bench files that import it are migrated

Headline changes

• @tuananh/sax-parser 1.6 has largely closed its chunked-streaming gap. It now takes both EPG columns in the streaming table (19,238 and 18,062 op/s), and its 64 B throughput exceeds its 256 B throughput, so per-write bridge cost is effectively gone. Eksml holds RSS (3.7x), POM, and attr-heavy. In tokenization it is now clear second on EPG/POM with Eksml's lead as thin as 1.05x on the 64 B stress.
• Serialization: Eksml now leads every fixture with and without validation. Previous table had tXml edging small and EPG at default validation; 0.2.0's writer gains flipped both.
• DOM parsing unchanged in shape: Eksml 1.7-1.9x ahead of txml 6 everywhere it can parse.

Still true

• txml 6 still crashes on the RSS fixture: it hardcodes <link> as an HTML void element and RSS channels require <link>, so the -- cells and crash notes stay.
• The tokenize arity policing from a3c7528 already covers 1.6's zero-arity fast path; the note now documents it explicitly.

844 tests pass. All benches run clean (32/32 suites).