[Feat] Improved LangChain Callback Handler

[dot-agi]

📥 Pull Request

📘 Description

• Fixes [Bug]: LangChain callback handler on_llm_start/end issue #656
• Adds new methods on_chat_model_start and on_llm_new_token based on the latest callbacks docs
• Adds logic in case key is not found when retrieving events
• Parses SystemMessage and HumanMessage to ChatML format
• Adds logic to check if the completions is not similar to the message content
• Updates the _test_langchain_handler.py file to use the latest langchain release APIs

🧪 Testing
Tested using the notebook and updated langchain testing file

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 71 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
agentops/partners/langchain_callback_handler.py	0.00%	71 Missing ⚠️

📢 Thoughts on this report? Let us know!

[areibman]

Notebook run looks great, approved!