Importing langchain takes too long

[jianzs]

The example "langchain-llama2-chatbot-sagemaker-python" creates a llama2 conversational chatbot using AWS and LangChain. When deploying it on AWS, the initial execution might time out. The issue we've identified is that importing LangChain is taking too long, about 50 seconds, even with .pyc files available. However, after the initial import, subsequent executions run smoothly.

We need to find why the initial import is taking so long and fix it.