test(react-overflow): rewrite paint-probe as a paint-only opt-out matrix

Measure only what reaches the screen: a plain requestAnimationFrame loop,
decoupled from React's render/commit/effect cycle, records a filmstrip of every
painted frame. Covers all four opt-out combinations (item/menu x in/out) and
asserts the stable anchors — the first painted frame and the converged final
frame — leaving the timing-dependent intermediate (a transient menu-count
flicker) unasserted so the test does not flake.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: bsunderhus