Add unit tests for service functionality and model caching

- Implement tests for ben2 and da3 model caching to ensure models are reused for matching runtime keys.
- Verify service state management, including client registration, job cancellation, and client expiration.
- Test discovery file creation and removal based on service ownership.
- Ensure frame extraction functionality works without models and produces expected results.

src/snapform/preferences.py

@@ -2,7 +2,7 @@ from pathlib import Path
 
 import bpy
 
-from .runtime import device_enum_items
+from .client import device_enum_items
 
 
 class SnapFormPreferences(bpy.types.AddonPreferences):
@@ -11,7 +11,7 @@ class SnapFormPreferences(bpy.types.AddonPreferences):
     storage_root: bpy.props.StringProperty(
         name="Storage Root",
         description=(
-            "Shared user-writable storage for Backend Environment, models and jobs; "
+            "Shared user-writable storage for the environment, models and jobs; "
             "all Blender versions can use the same directory"
         ),
         subtype="DIR_PATH",
@@ -29,27 +29,27 @@ class SnapFormPreferences(bpy.types.AddonPreferences):
 
     def draw(self, _context):
         from .operators import active_job
-        from .runtime import runtime_directory, runtime_ready
+        from .client import venv_directory, env_installed
 
         layout = self.layout
         layout.prop(self, "storage_root")
         layout.prop(self, "device")
         layout.separator()
-        layout.label(text=f"Backend Environment: {runtime_directory()}")
-        if runtime_ready():
-            layout.label(text="Backend Environment is ready", icon="CHECKMARK")
+        layout.label(text=f"Environment: {venv_directory()}")
+        if env_installed():
+            layout.label(text="Environment is installed", icon="CHECKMARK")
         else:
             install_row = layout.row()
             install_row.enabled = active_job() is None
             operator = install_row.operator(
                 "snapform.run_job",
-                text="Install Backend",
+                text="Install Environment",
                 icon="IMPORT",
             )
-            operator.job_type = "INSTALL_RUNTIME"
+            operator.job_type = "INSTALL_ENV"
         layout.separator()
         operator = layout.operator(
-            "snapform.control_host",
+            "snapform.control_service",
             text="Open Service Log",
             icon="TEXT",
         )