Fix Amazon Nova support (use StrOutputParser) (#1202)

* use StrOutputParser in default chat

* encourage using StrOutputParser in docs

* pre-commit

Author: dlqqq

docs/source/developers/index.md

@@ -492,7 +492,7 @@ def create_llm_chain(
         prompt_template = FIX_PROMPT_TEMPLATE
         self.prompt_template = prompt_template
 
-        runnable = prompt_template | llm  # type:ignore
+        runnable = prompt_template | llm | StrOutputParser()  # type:ignore
         self.llm_chain = runnable
 ```
 

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

@@ -3,6 +3,7 @@
 
 from jupyter_ai_magics.providers import BaseProvider
 from jupyterlab_chat.models import Message
+from langchain_core.output_parsers import StrOutputParser
 from langchain_core.runnables.history import RunnableWithMessageHistory
 
 from ..context_providers import ContextProviderException, find_commands
@@ -36,7 +37,7 @@ def create_llm_chain(
         self.llm = llm
         self.prompt_template = prompt_template
 
-        runnable = prompt_template | llm  # type:ignore
+        runnable = prompt_template | llm | StrOutputParser()  # type:ignore
         if not llm.manages_history:
             runnable = RunnableWithMessageHistory(
                 runnable=runnable,  #  type:ignore[arg-type]