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/nodes/arrangement/arrange.py

@@ -4,7 +4,7 @@ from .branches import calculation_blocks
 from .dimensions import estimate_node_dimensions, visible_socket
 from .flow import origin_socket, socket_links
 from .layout import plan_layout
-from ..common.nodes import prepare_node_group, replace_link_source
+from nodes.common.nodes import prepare_node_group, replace_link_source
 
 
 def _remove_routes(node_group):