Switch to WebGPU

[DraTeots]

WebGPU is an old new technology that is now supported by all major browsers (including Safari) and three.js. The rationale:

• GPU-driven rendering — WebGPU compute shaders can handle instanced hit rendering (thousands of BoxHits) entirely on GPU, reducing CPU overhead
• Compute-based BVH traversal — move raycasting/picking from CPU to GPU compute shaders, significantly faster for large geometries
• Better batching — WebGPU's bind group model reduces draw call overhead vs WebGL's per-uniform state changes, helping with merged detector geometries
• GPU-side time filtering — painters currently filter hits/trajectories by time on CPU; a compute shader could cull/animate thousands of objects per frame with near-zero CPU cost
• Indirect rendering — GPU can decide what to draw (frustum culling, LOD selection) without CPU roundtrips, critical for full-detector views
• Parallel geometry processing — geometry optimization/merging steps could run as compute passes during load
• Modern pipeline state — explicit pipeline objects avoid WebGL's hidden state validation overhead, more predictable frame times
• Larger buffers — WebGPU supports storage buffers well beyond WebGL's uniform buffer limits, enabling bigger event datasets in GPU memory