Optimize and robustify asset prefetching and material loading.

- Parallelize asset prefetching (max 4 workers) with retry logic and on-screen error banner, replacing silent failures and cryptic WASM out-of-bounds crashes with explicit missing-file errors.
- Support binary Uint8Array/ArrayBuffer in C++ asset registry via typed_memory_view, preventing Embind string coercion from corrupting binary shader packages into ASCII text.
- Automatically glob .mat files in CMake instead of maintaining a manual list.
- Add missing reflection materials to prefetch arrays.
- Disable caching for index.html in web server so template/script updates apply on normal page reload without stale cache issues, the file is small so caching had a negligible upside.
- Add null resource and payload validation in ObjectManager::LoadMaterial before constructing Filament materials.

PiperOrigin-RevId: 963364509
Change-Id: I7de79df6a5cede4e54683415ee193f1c5a665286

python/mujoco/experimental/studio/web/web_server.py

@@ -479,8 +479,12 @@ def _run_server(
     content_type = _CONTENT_TYPES.get(
         os.path.splitext(full)[1], "application/octet-stream"
     )
+    cacheable = not rel.endswith("index.html")
     return Response(
-        200, "OK", _http_headers(content_type, len(body), cacheable=True), body
+        200,
+        "OK",
+        _http_headers(content_type, len(body), cacheable=cacheable),
+        body,
     )
 
   async def main_loop() -> None: