Body sync, world events, mouse hover, world sort and batch assembly of
plain nodes run in C, reading node fields via cached atoms (~4 ns/read).
Special nodes are handed back to JS through a callback, so frame order is
unchanged; native_passes_test compares C and JS frames byte for byte.
The tilemap Y-sort hook is now active only with a ysort map.

Release, 2000 nodes: sprites 6.9 -> 2.1 ms, bodies 6.6 -> 2.3,
tweens 10.3 -> 4.2, $.batch 13.5 -> 5.1.

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