Copybara import of the project:

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9d63ebca419496e36f94fbfec6f97f0227846cf5 by Balint-H <bkh16@ic.ac.uk>:

Throw exception if OBJ file is referenced in MJCF when loading in Unity

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a50486c19a3483cd914e7957d7d4a5efaab9d977 by Balint-H <bkh16@ic.ac.uk>:

Adjust line length

COPYBARA_INTEGRATE_REVIEW=https://github.com/google-deepmind/mujoco/pull/2248 from Balint-H:fix/unity-obj-warning a50486c19a3483cd914e7957d7d4a5efaab9d977
PiperOrigin-RevId: 699962619
Change-Id: I2edff691fd5cedf79e2564f2ac5f2115393a4bf6

unity/Editor/Importer/MjImporterWithAssets.cs

@@ -152,6 +152,13 @@ public class MjImporterWithAssets : MjcfImporter {
       parentNode.GetStringAttribute("name", defaultValue: string.Empty);
     var assetReferenceName = MjEngineTool.Sanitize(unsanitizedAssetReferenceName);
     var sourceFilePath = Path.Combine(_sourceMeshesDir, fileName);
+
+    if (Path.GetExtension(sourceFilePath) == ".obj") {
+      throw new NotImplementedException("OBJ mesh file loading is not yet implemented. " +
+                                        "Please convert to binary STL. " +
+                                        $"Attempted to load: {sourceFilePath}");
+    }
+
     var targetFilePath = Path.Combine(_targetMeshesDir, assetReferenceName + ".stl");
     if (File.Exists(targetFilePath)) {
       File.Delete(targetFilePath);