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.

tools/pack.py

@@ -35,6 +35,15 @@ PLATFORM_CONFIGS = {
 PLATFORMS = tuple(PLATFORM_CONFIGS)
 
 
+def require_node_asset():
+    """Fail before packaging when the generated node asset is absent."""
+    asset_path = SOURCE_DIR / "assets" / "O_AnyImage.blend"
+    if not asset_path.is_file():
+        raise RuntimeError(
+            "Node asset is missing; run: uv run --group blender node-group build"
+        )
+
+
 def project_dependencies():
     """Return Extension wheel requirements declared by the project."""
     project = tomllib.loads(
@@ -171,6 +180,7 @@ def manifest_for_platform(platform, wheels):
 
 
 def _build_extension(platform, wheels):
+    require_node_asset()
     wheels = extension_wheels(wheels)
     manifest_text = manifest_for_platform(platform, wheels)
     manifest = tomllib.loads(manifest_text)