Prevent queuing lots of setTypingState

@futurize() is now called with parentheses and can take a max_instances
int argument. This is used for setTypingState to not have more than one
queued calls per room and True/False state and avoids bombing the server
with old ephemeral events after a network loss and reconnection.

harmonyqml/backend/backend.py

@@ -48,7 +48,7 @@ class Backend(QObject):
 
     @pyqtSlot(str, result="QVariant")
     @pyqtSlot(str, bool, result="QVariant")
-    @futurize
+    @futurize()
     def getUserDisplayName(self, user_id: str, can_block: bool = True) -> str:
         if user_id in self._queried_displaynames:
             return self._queried_displaynames[user_id]