tests: proper handling of event loops

Event loops have to be closed properly, otherwise pytest will throw a
warning / error. Disconnecting clients and closing the server is
important for that, as well as stopping tasks.
Additionally, I had to add loop_scope parameters to share the event loop
throughout modules which all use the same pydase.Server instance.

tests/utils/serialization/test_serializer.py

@@ -207,7 +207,7 @@ def test_ColouredEnum_serialize() -> None:
     }
 
 
-@pytest.mark.asyncio(scope="module")
+@pytest.mark.asyncio(loop_scope="module")
 async def test_method_serialization() -> None:
     class ClassWithMethod(pydase.DataService):
         def some_method(self) -> str: