feat: Add BEN2 background removal functionality and integrate into SnapForm

- Introduced BEN2 model for background removal in the panel and properties.
- Updated runtime to handle background removal commands and model downloads.
- Implemented background removal logic in worker, including image processing and saving results.
- Enhanced tests to cover new background removal features and ensure proper integration.
- Updated version to 0.9.28 to reflect new features and improvements.

src/snapform/__init__.py

@@ -1,8 +1,11 @@
 import bpy
 
 from .image_depth import (
+    ApplyRemovedBackground,
     BuildDepthPlane,
+    BuildOriginalDepthPlane,
     ConvertImageToDepthPlane,
+    RemoveImageBackground,
     draw_image_context_menu,
 )
 from .operators import (
@@ -22,7 +25,10 @@ CLASSES = (
     SnapFormSettings,
     RunJob,
     CancelJob,
+    ApplyRemovedBackground,
+    RemoveImageBackground,
     BuildDepthPlane,
+    BuildOriginalDepthPlane,
     ConvertImageToDepthPlane,
     RuntimeModelsPanel,
     DebugPanel,