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.

openspec/changes/separate-node-sources-and-tools/specs/maintainable-project-structure/spec.md

@@ -0,0 +1,21 @@
+## MODIFIED Requirements
+
+### Requirement: Node asset modules reflect responsibilities
+
+根目录 `nodes/` 的模块 MUST 只包含节点组及其共用构建定义，`tools/nodes/` MUST 只包含构建入口、布局、资产校验和预览工具。所有移动 MUST 同步导入、wheel 包清单、构建与验证入口及测试路径，并删除旧路径和转发层。
+
+#### Scenario: Load reorganized node definitions
+- **WHEN** 构建工具和节点行为测试导入节点组定义
+- **THEN** 导入指向 `nodes.groups` 或 `nodes.common`，不存在 `tools.nodes.groups` 或 `tools.nodes.common` 兼容路径
+
+#### Scenario: Load node asset tools
+- **WHEN** 启动器加载节点构建、布局、验证或预览模块
+- **THEN** 工具从 `tools.nodes` 加载，并从顶层 `nodes` 包使用节点定义
+
+#### Scenario: Preserve node behavior
+- **WHEN** 对重组后的节点构建函数运行针对性测试
+- **THEN** 节点组名称、接口、默认值、运算、连接、布局和求值与重组前一致
+
+#### Scenario: Locate node tests
+- **WHEN** 维护者按测试路径查找节点相关覆盖
+- **THEN** 节点定义行为测试位于 `tests/nodes`，构建与资产工具测试位于 `tests/tools/nodes`