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/services/load3dService.ts

@@ -75,23 +75,36 @@ export class Load3dService {
     const sourceModel = source.modelManager.currentModel
 
     if (sourceModel) {
-      const modelClone = sourceModel.clone()
+      if (source.isSplatModel()) {
+        const originalURL = source.modelManager.originalURL
+        if (originalURL) {
+          await target.loadModel(originalURL)
+        }
+      } else {
+        const modelClone = sourceModel.clone()
 
-      target.getModelManager().currentModel = modelClone
-      target.getSceneManager().scene.add(modelClone)
+        target.getModelManager().currentModel = modelClone
+        target.getSceneManager().scene.add(modelClone)
 
-      target.getModelManager().materialMode =
-        source.getModelManager().materialMode
+        const sourceOriginalModel = source.getModelManager().originalModel
 
-      target.getModelManager().currentUpDirection =
-        source.getModelManager().currentUpDirection
+        if (sourceOriginalModel) {
+          target.getModelManager().originalModel = sourceOriginalModel
+        }
 
-      target.setMaterialMode(source.getModelManager().materialMode)
-      target.setUpDirection(source.getModelManager().currentUpDirection)
+        target.getModelManager().materialMode =
+          source.getModelManager().materialMode
 
-      if (source.getModelManager().appliedTexture) {
-        target.getModelManager().appliedTexture =
-          source.getModelManager().appliedTexture
+        target.getModelManager().currentUpDirection =
+          source.getModelManager().currentUpDirection
+
+        target.setMaterialMode(source.getModelManager().materialMode)
+        target.setUpDirection(source.getModelManager().currentUpDirection)
+
+        if (source.getModelManager().appliedTexture) {
+          target.getModelManager().appliedTexture =
+            source.getModelManager().appliedTexture
+        }
       }
     }