fix: 🚑 remove thought_signature from events

Author: BloodBoy21

src/google/adk/sessions/redis_memory_session_service.py

@@ -137,14 +137,22 @@ async def append_event(self, session: Session, event: Event) -> Event:
           self.cache.hset(
               f"{State.USER_PREFIX}{session.app_name}:{session.user_id}",
               key.removeprefix(State.USER_PREFIX),
-              json.dumps(value),
+              json.dumps(self.clean_event(event)),
           )
 
     sessions = self._load_sessions(session.app_name, session.user_id)
     sessions[session.id] = session.to_dict()
     self._save_sessions(session.app_name, session.user_id, sessions)
 
     return event
+  
+  def clean_event(self,event):
+    for event in event["events"]:
+      if event["content"] is None:
+        continue
+      for part in event["content"]["parts"]:
+        part.pop("thought_signature")
+    return event
 
   def _merge_state(
       self, app_name: str, user_id: str, session: Session