fix memory leak issue

[WilliamLiu-1997]

Memory Leak Fix

Incomplete or missing dispose() methods cause GPU resources and large typed arrays to leak when SplatMesh instances are destroyed.

Changes

• SplatMesh.dispose() — Release cached DynoPrograms, SplatEdits, SplatSkinning, RgbaArray, LoD state, context refs, modifiers, and callbacks. Also clean up caches on generator rebuild.
• SparkRenderer.dispose() — Cancel pending timers, clear LoD tracking structures, dispose material/geometry. Add unregisterMesh() to clean up LoD entries from all active renderers.
• ExtSplats.dispose() — Dispose SH textures (sh1–sh3), clear extArrays and extra.
• PackedSplats.dispose() — Dispose SH textures, null out packedArray, clear extra.
• SplatAccumulator / PackedSplats — Add releaseGeneratorProgram() to evict and dispose cached DynoProgram from static maps.
• DynoProgram — Add dispose() to release associated ShaderMaterial.
• SplatEdits — Add dispose() to release SDF DataArrayTexture.
• SplatSkinning — Add dispose() to release skin/bone DataTextures.

[WilliamLiu-1997]

Here are examples：

Example that fixed memory leak
https://threejs-3d-tiles-renderer-mynn6oxso-williamliu1997s-projects.vercel.app/

Example that show memory leak (you can see the memory usage in red memory panel, in this example, as you look around, zoom in/out, the memory usage will keep inscreasing)
https://threejs-3d-tiles-renderer-dq57u8e0s-williamliu1997s-projects.vercel.app/

Memory Leak Example

### Memory Leak Fixed Example