Speed up BVH parsing and frame channel lookups

[FranklinTaoTao]

Summary

This PR improves BVH parsing and query performance by optimizing tokenization and frame/channel access.

Changes

• Replace character-by-character parsing with regex-based line/token splitting.
• Parse frame component values into floats once during tokenization.
• Add joint/channel caches to avoid repeated tree scans and channel index recalculation.
• Update frame accessors to return already-parsed float values directly.