chore: refactor pydantic v1 code

Author: maciejmajek

docs/developer_guide.md

@@ -67,7 +67,7 @@ See the example below.
 
 ```python
 from langchain.tools import tool, BaseTool
-from langchain.pydantic_v1 import BaseModel, Field
+from pydantic import BaseModel, Field
 from typing import Type
 from myrobot import robot
 

tests/messages/test_multimodal.py

@@ -26,8 +26,8 @@
 )
 from langchain_core.language_models.chat_models import BaseChatModel
 from langchain_core.messages import AIMessage, BaseMessage
-from langchain_core.pydantic_v1 import BaseModel, Field
 from langfuse.callback import CallbackHandler
+from pydantic import BaseModel, Field
 from pytest import FixtureRequest
 
 from rai.messages import HumanMultimodalMessage