feat(selection): separate selection geometry from image content processing

- Introduced a new design for selection rasterization that decouples the selection geometry from the image content, ensuring that the SelectionMask is independent of the source image's alpha and color.
- Updated the `rasterize_selection_path` function to only accept selection paths and image dimensions, removing parameters related to source alpha and alpha thresholds.
- Implemented a new approach for handling selection paths using non-zero winding fill, ensuring overlapping areas are preserved.
- Enhanced performance by utilizing a scanline algorithm for rasterization, significantly reducing processing time for high-resolution images.
- Updated internal documentation and added comprehensive tests to validate the new behavior and performance improvements.
- Ensured backward compatibility by maintaining existing interfaces where necessary while introducing breaking changes in the selection processing logic.

docs/internals/operators/clipboard-image.md

@@ -38,4 +38,4 @@ flowchart TD
 
 落点仍在 `actions.py` 中完成：3D View 创建 Reference 或 Plane，Node Editor 创建与当前节点树匹配的 Image 节点，绘制模式把 Image 配置为当前画笔的 Texture。鼠标位置和视图位置也在这里换算。
 
-Plane 路径调用 `convert_to_plane/mesh_plane.py` 创建基础网格，并从节点资产加载 `O Mesh Plane`。`actions.py` 创建 Blender 数据。
+Plane 路径调用 `convert_to_plane/mesh_plane.py` 创建中心原点基础网格，并从节点资产加载 `O Mesh Plane`。`actions.py` 创建图像材质并放入 Mesh 第 `0` 个材质槽，节点组只生成几何。