- animationUpdate now advances and resolves boundary crossings for
ANIMATION_FLAG_LOOP, ANIMATION_FLAG_PINGPONG, ANIMATION_FLAG_REVERSE, and
the STOP_BEGINNING/STOP_END flags, firing onLoop/onComplete appropriately;
guards against LOOP+PINGPONG being set together and moves the
duration-must-be-positive check into animationInit
- keyframeGetValue clamps to the last keyframe's value instead of dividing
by zero once time reaches it, and its keyframe walk drops a branch that's
unreachable after that clamp
- Adds test/animation/test_animation.c covering init, per-layer sampling,
and the full animationUpdate flag matrix
