fix(types): resolve pre-existing basedpyright errors in tests

Fix ~790 basedpyright errors across the test suite:
- Type stub subclasses of real production classes with super().__init__()
- Add missing generic type arguments and Dict[str, Any] annotations
- Add None guards before subscript/member access
- Adapt tests to production API changes (removed dead handlers,
  PersistentModelCache.get_default, _i18n_filter_added location)

tests/services/test_download_manager_basic.py

@@ -758,6 +758,7 @@ async def test_get_active_downloads_restores_orphaned_aria2_partial_as_paused(
 
     downloads = await manager.get_active_downloads()
     persisted = await manager._aria2_state_store.get("download-1")
+    assert persisted is not None
 
     assert downloads["downloads"] == [
         {
@@ -922,6 +923,7 @@ async def test_get_active_downloads_restores_persisted_aria2_without_initial_sav
 
     downloads = await manager.get_active_downloads()
     persisted = await manager._aria2_state_store.get("download-1")
+    assert persisted is not None
 
     assert downloads["downloads"] == [
         {