Call `NWCServer.event_handler_task.cancel()` on asyncio thread.
```
File "/home/user/Documents/electrum/electrum/plugins/nwc/nwcserver.py", line 281, in restart_event_handler
self.event_handler_task.cancel()
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib64/python3.14/asyncio/base_events.py", line 829, in call_soon
self._check_thread()
~~~~~~~~~~~~~~~~~~^^
File "/usr/lib64/python3.14/asyncio/base_events.py", line 866, in _check_thread
raise RuntimeError(
"Non-thread-safe operation invoked on an event loop other "
"than the current one")
RuntimeError: Non-thread-safe operation invoked on an event loop other than the current one
```
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