fix: close mcp client event loop

Author: David Padbury

src/strands/tools/mcp/mcp_client.py

@@ -638,8 +638,11 @@ def _background_task(self) -> None:
         """
         self._log_debug_with_thread("setting up background task event loop")
         self._background_thread_event_loop = asyncio.new_event_loop()
-        asyncio.set_event_loop(self._background_thread_event_loop)
-        self._background_thread_event_loop.run_until_complete(self._async_background_thread())
+        try:
+            asyncio.set_event_loop(self._background_thread_event_loop)
+            self._background_thread_event_loop.run_until_complete(self._async_background_thread())
+        finally:
+            self._background_thread_event_loop.close()
 
     def _map_mcp_content_to_tool_result_content(
         self,