Gaussian Splat Optimization

[danielzhong]

Description

This PR applies profile driven optimizations to Gaussian splat loading and update.

Main changes:

• Adds a fast path and transform caching in GaussianSplatPrimitive.transformTile to reduce per-splat matrix/TRS work
• Preserves original glTF attribute data in GaussianSplat3DTileContent and keeps transformed copies separate for correct rebuild behavior
• Reuses aggregate snapshot buffers for positions, scales, rotations, and colors to reduce allocation churn and GC pressure
• Makes steady-state sorting less aggressive during camera movement to reduce repeated sort work

These changes were based on Chrome profiling, where the main hotspots were transform work, repeated large allocations, and repeated scheduling/cloning during texture generation and sorting. The goal is to reduce CPU time and GC pressure during Gaussian splat loading and runtime updates.

Before:

After:

Issue number and link

Testing plan

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @danielzhong!

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