3dgs & ply support (#7602)

## Summary

integrated sparkjs https://sparkjs.dev/, built by [world labs
](https://www.worldlabs.ai/) to support 3dgs.

- Add 3D Gaussian Splatting (3DGS) support using @sparkjsdev/spark
library
- Add PLY file format support with multiple rendering engines
- Support new file formats: `.ply`, `.spz`, `.splat`, `.ksplat`
- Add PLY Engine setting with three options: `threejs` (mesh), `fastply`
(optimized ASCII point clouds), `sparkjs` (3DGS)
- Add `FastPLYLoader` for 4-5x faster ASCII PLY parsing
- Add `original(Advanced)` material mode for point cloud rendering with
THREE.Points

3dgs generated by https://marble.worldlabs.ai/

test ply file from:
1. made by https://github.com/PozzettiAndrea/ComfyUI-DepthAnythingV3
2. threejs offically repo

## Screenshots


https://github.com/user-attachments/assets/44e64d3e-b58d-4341-9a70-a9aa64801220



https://github.com/user-attachments/assets/76b0dfba-0c12-4f64-91cb-bfc5d672294d



https://github.com/user-attachments/assets/2a8bfe81-1fb2-44c4-8787-dff325369c61



https://github.com/user-attachments/assets/e4beecee-d7a2-40c9-97f7-79b09c60312d

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7602-3dgs-ply-support-2cd6d73d3650814098fcea86cfaf747d)
by [Unito](https://www.unito.io)

src/components/load3d/Load3dViewerContent.vue

@@ -46,6 +46,8 @@
             <ModelControls
               v-model:up-direction="viewer.upDirection.value"
               v-model:material-mode="viewer.materialMode.value"
+              :hide-material-mode="viewer.isSplatModel.value"
+              :is-ply-model="viewer.isPlyModel.value"
             />
           </div>
 
@@ -56,13 +58,13 @@
             />
           </div>
 
-          <div class="space-y-4 p-2">
+          <div v-if="!viewer.isSplatModel.value" class="space-y-4 p-2">
             <LightControls
               v-model:light-intensity="viewer.lightIntensity.value"
             />
           </div>
 
-          <div class="space-y-4 p-2">
+          <div v-if="!viewer.isSplatModel.value" class="space-y-4 p-2">
             <ExportControls @export-model="viewer.exportModel" />
           </div>
         </div>