Add native spring easing for motion and style transitions

[Ernxst]

Fixes #196.

Summary

• add the shared { type: "spring", stiffness?, damping?, mass?, velocity? } easing object to both MotionTransition.ease and StyleTransition.easing
• drive motion and state-style springs through native closed-form damped-spring tracks, preserving the painted position and per-channel velocity when interrupted
• derive spring completion from unit-aware settling thresholds, keep delay semantics, and ignore fixed duration for springs
• reject unknown spring tags, unknown fields, and invalid physical parameters through the existing motion/style rejection paths
• document the browser mirror as sampled CSS linear() easing

The object wire format deliberately matches remorses/gpuix#34 for reconciliation, while this implementation keeps the existing native track machinery and adds no JavaScript frame loop. Defaults are Motion's 100 / 10 / 1, and springs are available on both motion targets and state-style transitions.

Verification

• bun run build --target aarch64-apple-darwin in packages/native
• bun run test in packages/react: 719 passed, 0 failed, 0 skipped (42 files)
• bun run test in examples: 54 passed, 0 failed, 0 skipped (7 files)
• cargo test --lib in packages/native: 344 passed, 0 failed, 0 ignored
• fail-before: the initial four native spring specs failed 0/4 and the state-style binding test snapped directly to its target; pass-after: eight targeted native spring regressions and both React spring effect tests pass