Add immutable native YCD animation samplers

[Hancapo]

Summary

• Add YcdAnimation.compile() and the public immutable YcdAnimationSampler, retaining the existing typed evaluate_tracks call shape.
• Copy decoded channel cycles into owned native buffers, evaluate under a released GIL, and construct only final Vector4/Quaternion values.
• Preserve integer/fractional behavior, track filtering, missing keys, cyclic channels, physical block overlap, and cached quaternion reconstruction after scalar interpolation.
• Keep editable model behavior unchanged. Compiled samplers intentionally do not observe later edits; recompile explicitly. No global frame/plan cache or source object retention.
• Share decoded channel extraction with precision validation rather than introducing another binary decoder.

Validation

• Synthetic differential tests cover both editions, opcode 7/8 layouts, out-of-range seeks, empty/default/indirect channels, missing keys, source edits, concurrent evaluations and final-only typed construction.
• Uninstrumented 196-track test: mutable evaluation 1.719 ms/frame, compiled evaluation 0.120 ms/frame; approximately 14x faster. Copied sample storage: 947776 bytes. This is library-only timing, not a viewer FPS prediction.

The following PR will expose clip-level snapshots and add external corpus coverage. No consumer application, installed package, game executable or assets are changed.