Validate gameplay services

Back to Use gameplay actions.

Library tests cover easing endpoints/overshoot, timing/sequence leftovers, path geometry and traversal, pause/reverse/repeat, ownership/reload/signal cleanup, physics contacts, PCM mixing, clip sampling/blends/markers, IK, glTF/FBX import, and live skeletal vertex deformation. The integration fixture executes shared math, tween/timer callbacks and animation playback/markers in all ten script types. RUSTIC_REQUIRE_ALL_SDKS=1 makes a missing toolchain fail that fixture.