use existing multiprocessing import

Author: rodja

nicegui/native/native_mode.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import _thread
-import multiprocessing
 import multiprocessing as mp
 import queue
 import socket
@@ -93,8 +92,8 @@ def window_method_executor() -> None:
             except Exception:
                 log.exception(f'error in window.{method_name}')
         # NOTE: we need to cleanup the multiprocessing queues, see https://github.com/zauberzeug/nicegui/issues/4131
-        if hasattr(multiprocessing.util, '_exit_function'):  # to make mypy happy
-            multiprocessing.util._exit_function()  # pylint: disable=protected-access
+        if hasattr(mp.util, '_exit_function'):  # to make mypy happy
+            mp.util._exit_function()  # pylint: disable=protected-access
 
     Thread(target=window_method_executor).start()