Clear both chat history and conversation memory

(1) Updated `clear.py` to clear chat history and display the help command again.
(2) Updated `base.py` to remove conversation memory when chat history is cleared.

packages/jupyter-ai/jupyter_ai/chat_handlers/base.py

@@ -267,7 +267,10 @@ def get_llm_chain(self):
         if not lm_provider or not lm_provider_params:
             return None
 
-        if curr_lm_id != next_lm_id:
+        if len(self._chat_history) <= 2: # Check if chat history has been cleared, then reinitialize the llm chain
+            self.log.info("Clear conversation memory, re-initializing the llm chain.")
+            self.create_llm_chain(lm_provider, lm_provider_params)      
+        elif curr_lm_id != next_lm_id:
             self.log.info(
                 f"Switching chat language model from {curr_lm_id} to {next_lm_id}."
             )

packages/jupyter-ai/jupyter_ai/chat_handlers/clear.py

@@ -19,14 +19,15 @@ def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     async def process_message(self, _):
-        tmp_chat_history = self._chat_history[0]
-        self._chat_history.clear()
         for handler in self._root_chat_handlers.values():
             if not handler:
                 continue
 
             handler.broadcast_message(ClearMessage())
 
+            tmp_chat_history = self._chat_history[0]
+            self._chat_history.clear()
+
             self._chat_history = [tmp_chat_history]
             self.reply(tmp_chat_history.body)