Add comprehensive tests for image processing nodes and refactor node imports

- Introduced new test files for image layer, image plane, normal scale, object normal rotation, shadeless, and temporary attributes.
- Implemented tests to validate the behavior of alpha curves, depth layers, and normal scales in various rendering engines.
- Refactored import paths for node groups to align with the new directory structure.
- Added checks for temporary attribute lifetimes and ensured proper cleanup without warnings.
- Enhanced CLI commands to require the Blender group and validate the presence of generated node assets before packaging.
- Updated packaging scripts to enforce the existence of necessary assets, preventing build failures.

tests/tools/test_pack.py

@@ -42,6 +42,16 @@ class ArchiveContents:
 
 
 class ExtensionPackagingTest(unittest.TestCase):
+    def test_rejects_missing_generated_node_asset(self):
+        pack = load_pack()
+        with tempfile.TemporaryDirectory() as directory:
+            with patch.object(pack, "SOURCE_DIR", Path(directory)):
+                with self.assertRaisesRegex(
+                    RuntimeError,
+                    "uv run --group blender node-group build",
+                ):
+                    pack._build_extension("windows-x64", [])
+
     def test_selects_platform_archive_contents_and_manifest(self):
         pack = load_pack()
         records = {}