system.py: Async functions should not call time.sleep

* #771
* https://docs.astral.sh/ruff/rules/blocking-sleep-in-async-function
* https://docs.astral.sh/ruff/rules/module-import-not-at-top-of-file

Author: cclauss

mavsdk/system.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import asyncio
 import logging
 import threading
 
@@ -107,12 +108,13 @@ async def connect(self, system_address=None):
         """
 
         if self._server_process is not None:
-            # a mavsdk_server have already been launch by this instance:
+            # a mavsdk_server has already been launched by this instance:
             # --> clean all before trying to reconnect
             self._stop_mavsdk_server()
 
-            # add a delay to be sure recourses have been freed and restart mavsdk_server
-            import time; time.sleep(1)
+            # add a delay to be sure resources have been freed and restart mavsdk_server
+            await asyncio.sleep(1)
+            
 
         if self._mavsdk_server_address is None:
             self._mavsdk_server_address = 'localhost'