Refactor and enhance geometry node groups for depth plane and material layers

- Updated the depth plane node group to load from an asset and simplified the interface.
- Created a new build script for depth plane geometry nodes.
- Introduced material layer groups for image and depth materials with appropriate sockets.
- Added functionality to connect balloon normal scale to the image material.
- Enhanced tests to validate the new node groups and their connections.
- Ensured that production code does not create node groups directly.

tests/test_node_assets.py

@@ -0,0 +1,32 @@
+import unittest
+from pathlib import Path
+
+
+PROJECT_ROOT = Path(__file__).resolve().parents[1]
+SOURCE_ROOT = PROJECT_ROOT / "src" / "anyimage"
+
+
+class NodeAssetTest(unittest.TestCase):
+    def test_production_code_does_not_create_node_groups(self):
+        offenders = []
+        for path in SOURCE_ROOT.rglob("*.py"):
+            if "bpy.data.node_groups.new" in path.read_text(encoding="utf-8"):
+                offenders.append(path.relative_to(PROJECT_ROOT).as_posix())
+        self.assertEqual(offenders, [])
+
+    def test_runtime_node_group_entries_load_assets(self):
+        material_source = (
+            SOURCE_ROOT / "operators" / "common" / "mesh_result.py"
+        ).read_text(encoding="utf-8")
+        plane_source = (
+            SOURCE_ROOT / "operators" / "convert_to_plane" / "nodes.py"
+        ).read_text(encoding="utf-8")
+        self.assertIn("return load_asset_node_group(group_name)", material_source)
+        self.assertIn(
+            "return load_asset_node_group(DEPTH_PLANE_NODE_GROUP_NAME)",
+            plane_source,
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()