feat(node_assets): add image plane geometry nodes and validation scripts

- Implemented `image_plane.py` to build the Image Plane Geometry Nodes group with customizable parameters for geometry, subdivide, and thickness.
- Created `image_plane_validation.py` to validate the functionality of the image plane, ensuring correct geometry generation and material assignment.
- Developed `material_layers.py` to construct shader node groups for image materials, including depth and normal handling.
- Authored `plane_layouts.py` to define node arrangements for image geometry assets.
- Introduced `shadeless.py` to create a shadeless shader node group that displays color without scene lighting while preserving shadows and reflections.

tests/test_clipboard_image.py

@@ -6,6 +6,7 @@ import unittest
 from pathlib import Path
 from types import ModuleType, SimpleNamespace
 from unittest.mock import Mock, patch
+from blender_test_support import mock_bpy_imports
 
 
 PROJECT_ROOT = Path(__file__).resolve().parents[1]
@@ -15,6 +16,10 @@ sys.path.insert(0, str(PROJECT_ROOT / "src"))
 class ClipboardImageTest(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
+        cls.previous_addon_modules = {
+            name: module for name, module in sys.modules.items()
+            if name == "anyimage" or name.startswith("anyimage.")
+        }
         cls.temporary_directory = tempfile.TemporaryDirectory()
         cls.remove_anyimage_modules()
         fake_bpy = ModuleType("bpy")
@@ -47,7 +52,9 @@ class ClipboardImageTest(unittest.TestCase):
             )
         )
         fake_bpy.data = SimpleNamespace()
-        sys.modules["bpy"] = fake_bpy
+        cls.bpy_import_patch = mock_bpy_imports(fake_bpy)
+        cls.bpy_import_patch.start()
+        cls.addClassCleanup(cls.bpy_import_patch.stop)
         cls.fake_bpy = fake_bpy
 
         cls.addon = ModuleType("anyimage")
@@ -64,9 +71,9 @@ class ClipboardImageTest(unittest.TestCase):
 
     @classmethod
     def tearDownClass(cls):
-        sys.modules.pop("bpy", None)
         cls.remove_anyimage_modules()
         cls.temporary_directory.cleanup()
+        sys.modules.update(cls.previous_addon_modules)
 
     def test_operators_use_anyimage_prefix_and_plain_properties(self):
         clipboard_image = self.addon.clipboard_image