Add operators for model downloading and surface generation

- Implemented `DownloadModel` and `DownloadRequiredModels` operators for downloading models.
- Created `ClearModels` operator to clear model resources.
- Added `ConvertToSurface` operator for converting image empties into textured surfaces.
- Introduced `GenerateDa3Surface` and `GenerateMoge2Surface` operators for generating surfaces using DA3 and MoGe-2 models respectively.
- Developed utility functions for handling image mesh data, assigning attributes, and managing geometry nodes.
- Established runtime configuration and post-installation model downloading in `runtime.py`.

tests/test_pack.py

@@ -61,8 +61,10 @@ class PackTest(unittest.TestCase):
 
                 self.assertIn("__init__.py", names)
                 self.assertIn("blender_manifest.toml", names)
-                self.assertIn("blender/depth_plane.py", names)
-                self.assertIn("blender/surface.py", names)
+                self.assertIn("operators/depth_plane/operator.py", names)
+                self.assertIn("operators/image.py", names)
+                self.assertIn("operators/balloon/operator.py", names)
+                self.assertIn("operators/surface.py", names)
                 self.assertIn(
                     "assets/O_SnapForm.blend",
                     names,