openai and litellm version confilicts

[zhaochenyang20]

In the project.toml, we do not require a specific version of openai and litellm. If a user directly runs pip install ., then the newest version of openai may not support import openai.error. However, we use this in our api_tools.py. If we choose to use a lower version of openai, it is not supported by litellm. Thus we need to refactor our api_tools.py to support new version of openai and litellm.