The registry index (all/by_tag/by_class/facets) is built in C; nodes keep
a class_list array mirroring the classes Set. Constant node defaults move
to Node.prototype, tag colours are computed once per tag, addClass has a
regexp-free fast path, colour strings are cached. Multi-node .remove()
compacts the registry once; single drops search from the end.

churn:2000 6.2 -> 3.4 ms, $.batch:2000 5.1 -> 3.4 ms (Release).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>