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/models.py

@@ -9,6 +9,7 @@ class ModelSpec:
     license_name: str
     description: str
     supports_gs: bool
+    download_patterns: tuple[str, ...] = ()
 
 
 MODELS = {
@@ -53,6 +54,17 @@ MODELS = {
         supports_gs=True,
     ),
 }
+
+BEN2_MODEL = ModelSpec(
+    key="BEN2_BASE",
+    label="BEN2 Base",
+    repository="PramaLLC/BEN2",
+    license_name="MIT",
+    description="Fast high-quality background removal model",
+    supports_gs=False,
+    download_patterns=("config.json", "model.safetensors"),
+)
+DOWNLOADABLE_MODELS = {**MODELS, BEN2_MODEL.key: BEN2_MODEL}
 MODEL_NUMBERS = {
     model_key: number for number, model_key in enumerate(MODELS)
 }
@@ -123,3 +135,10 @@ def get_model(model_key):
         return MODELS[model_key]
     except KeyError as error:
         raise ValueError(f"Unknown DA3 model: {model_key}") from error
+
+
+def get_downloadable_model(model_key):
+    try:
+        return DOWNLOADABLE_MODELS[model_key]
+    except KeyError as error:
+        raise ValueError(f"Unknown model: {model_key}") from error