fix(backend): resolve circular import in file.py and remove deprecated params

- Defer WorkspaceManager import to inside store_media_file() to break circular import
- Remove deprecated return_content and save_to_workspace parameters (no callers)
- Make return_format a required parameter
- Update tests to use return_format

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

autogpt_platform/backend/backend/blocks/test/test_blocks_dos_vulnerability.py

@@ -239,6 +239,7 @@ class TestStoreMediaFileSecurity:
                     user_id="test_user",
                     graph_exec_id="test",
                 ),
+                return_format="for_local_processing",
             )
 
     @patch("backend.util.file.Path")
@@ -280,4 +281,5 @@ class TestStoreMediaFileSecurity:
                     user_id="test_user",
                     graph_exec_id="test",
                 ),
+                return_format="for_local_processing",
             )

autogpt_platform/backend/backend/util/file_test.py

@@ -245,4 +245,5 @@ class TestFileCloudIntegration:
                 await store_media_file(
                     file=MediaFileType(cloud_path),
                     execution_context=make_test_context(graph_exec_id=graph_exec_id),
+                    return_format="for_local_processing",
                 )