Add comprehensive tests for edge depth extension, empty image edits, and material view adaptation

- Introduced `test_edge_depth.py` to validate the functionality of edge depth extension, ensuring core alpha preservation, proper depth handling, and edge padding behavior.
- Created `test_empty_image_edits.py` to verify the behavior of image edits in Blender, focusing on shared edits, preservation of image properties, and handling of failed operations.
- Developed `test_material_view_adaptation.py` to test material adaptation preferences, ensuring color space and alpha settings are correctly applied and preserved across various scenarios.

tests/test_clipboard_image.py

@@ -30,6 +30,7 @@ class ClipboardImageTest(unittest.TestCase):
             StringProperty=lambda **options: options,
         )
         fake_bpy.types = SimpleNamespace(
+            AddonPreferences=object,
             GizmoGroup=object,
             Image=object,
             Menu=object,