Enhance device management and model handling in SnapForm

- Updated frame extraction logic to allow for single frame extraction.
- Integrated model readiness checks for BEN2 and DA3 models in relevant operators.
- Added directory name attribute to model specifications for better organization.
- Improved device selection logic for production and debug tasks.
- Refactored preferences to expose device settings and ensure they reflect available hardware.
- Enhanced runtime device detection and management, including support for CUDA and MPS.
- Updated tests to cover new device management features and model directory handling.
- Removed deprecated download model tests to streamline codebase.

src/snapform/image_depth.py

@@ -97,7 +97,7 @@ def extract_frame_range(source_object):
     )
     frame_count = (
         min(image_frames, total_frames)
-        if image_frames > 1
+        if image_frames >= 1
         else total_frames
     )
     start_frame = min(1 + frame_offset, total_frames - frame_count + 1)
@@ -1400,12 +1400,14 @@ class RemoveImageBackground(bpy.types.Operator):
     @classmethod
     def poll(cls, context):
         from .operators import active_job
-        from .runtime import host_busy
+        from .runtime import host_busy, model_ready
+        from .models import BEN2_MODEL
 
         return (
             is_image_empty(context.object)
             and active_job() is None
             and not host_busy()
+            and model_ready(BEN2_MODEL.key)
         )
 
     def execute(self, context):
@@ -1511,12 +1513,14 @@ class ConvertImageToDepthPlane(bpy.types.Operator):
     @classmethod
     def poll(cls, context):
         from .operators import active_job
-        from .runtime import host_busy
+        from .runtime import host_busy, model_ready
+        from .models import MODELS
 
         return (
             is_image_empty(context.object)
             and active_job() is None
             and not host_busy()
+            and any(model_ready(model_key) for model_key in MODELS)
         )
 
     def invoke(self, context, _event):
@@ -1535,6 +1539,9 @@ class ConvertImageToDepthPlane(bpy.types.Operator):
         return context.window_manager.invoke_props_dialog(self, width=340)
 
     def draw(self, context):
+        from .models import BEN2_MODEL
+        from .runtime import model_ready
+
         layout = self.layout
         layout.prop(self, "snapform_depth_source")
         if self.snapform_depth_source == "ESTIMATE":
@@ -1563,7 +1570,9 @@ class ConvertImageToDepthPlane(bpy.types.Operator):
         if settings_body is not None:
             settings_body.prop(self, "snapform_displacement_via")
             settings_body.prop(self, "snapform_subdivision_level")
-            settings_body.prop(self, "snapform_remove_background")
+            remove_background_row = settings_body.row()
+            remove_background_row.enabled = model_ready(BEN2_MODEL.key)
+            remove_background_row.prop(self, "snapform_remove_background")
             settings_body.prop(self, "snapform_unshaded")
         layout.prop(self, "snapform_delete_original")