Add _default_workspace to shared storage finalization

- Add _default_workspace to global vars
- Set _default_workspace to None on cleanup
- Ensure complete resource cleanup
- Fix missing workspace finalization

(cherry picked from commit 6d6716e9f8)

lightrag/kg/shared_storage.py

@@ -1456,7 +1456,8 @@ def finalize_share_data():
         _init_flags, \
         _initialized, \
         _update_flags, \
-        _async_locks
+        _async_locks, \
+        _default_workspace
 
     # Check if already initialized
     if not _initialized:
@@ -1522,5 +1523,6 @@ def finalize_share_data():
     _data_init_lock = None
     _update_flags = None
     _async_locks = None
+    _default_workspace = None
 
     direct_log(f"Process {os.getpid()} storage data finalization complete")