Simple node tweens with built-in easing run entirely in C (state, easing
table ported 1:1, writes incl. body position); JS resolves promises by id.
Effect timers (shake/flash/iframes) also native. Godot-style tween
scenarios stay in JS but skip per-frame totalDuration, per-frame target
dispatch and for-of iterators. nodes.c disables FMA contraction so results
match QuickJS bit for bit (caught by native_passes_test).

tween:2000 10.3 -> 2.9 ms; 2000 simple tweens 1.2 -> 0.04 ms per frame.

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