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.

docs/internals/development.md

@@ -27,7 +27,7 @@ Blender Stub 共用 `tests/support/blender.py`；Server 和实际 Blender 几何
 | --- | --- |
 | `uv run pack` | 生成 Windows、macOS arm64、Linux 扩展包 |
 | `uv run pack --prepare` | 为本机同步扩展 wheel 与 Manifest |
-| `uv run node-group build` | 构建、验证节点资产并运行测试 |
+| `uv run --group blender node-group build` | 构建、验证节点资产并运行节点测试 |
 | `uv run model sync` | 准备、校验并上传模型声明的文件 |
 | `uv run docs -dev` | 本地预览文档 |
 | `uv run docs` | 通过 Mike 发布项目版本并更新 latest |