Improve H.264 accelerated playback

[joaner]

Summary

• replace serial H.264 decoding with a bounded WebCodecs pipeline and drop stale rendered output under pressure
• preserve complete GOP dependencies and resynchronize only at safe IDR boundaries without clearing the last frame
• replace the misleading 64x-backed best-effort Max option with a deterministic 10x playback limit
• extend H.264 metrics, benchmarks, and regression coverage for multi-camera accelerated playback
• bump the package patch version to 1.7.5

Validation

• npm run typecheck
• npm run lint
• npm test -- --run (647 tests)
• npm run build
• H.264 Chromium E2E
• six-camera /Users/joaner/Downloads/test.mcap benchmarks at 1x, 4x, and 8x without decode, page, or console errors

Closes #29