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.

.github/workflows/test.yml

@@ -22,5 +22,8 @@ jobs:
         with:
           python-version: "3.11"
 
+      - name: Build node assets
+        run: uv run --group blender node-group build --skip-tests
+
       - name: Run tests
-        run: uv run --group blender pytest tests/anyimage tests/tools
+        run: uv run --group blender pytest tests/anyimage tests/nodes tests/tools