Add comprehensive tests for cutout and mesh functionalities

- Introduced `test_cutout.py` to validate cutout pie menu behavior, image lasso options, and mesh detail calculations.
- Added `test_mesh.py` to ensure correct tangent normal rasterization, plane source topology, and depth surface evaluations.
- Created `test_mesh_blender.py` to verify material node groups, tangent baking, and local cutout building from Blender images.
- Implemented tests for handling alpha regions and ensuring geometry nodes maintain expected behavior.

mkdocs.yml

@@ -16,6 +16,7 @@ nav:
   - 使用指南:
       - 选择转换方式: workflows.md
       - Image 编辑工具: image-tools.md
+      - Cutout: cutout.md
       - Mesh Plane: mesh-plane.md
       - Depth Plane: guide-depth-plane.md
       - Surface: guide-surface.md