Set Pantalaimon presence to offline

Before this change, Pantalaimon users would always appear online because
that is the default state when the /sync endpoint's set_presence
parameter is not set. By explicitly setting the parameter to "offline",
only the user-facing client (which executes its own /sync request)
affects the presence state.

pantalaimon/client.py

@@ -554,6 +554,7 @@ class PanClient(AsyncClient):
                 full_state=True,
                 since=next_batch,
                 loop_sleep_time=loop_sleep_time,
+                set_presence="offline",
             )
         )
         self.task = task