Add langchanin callback handler

[Dwij1704]

📥 Pull Request

• Closes Update LangChain Callback Handlers for v4 #687

📘 Description
This PR introduces the LangChain callback handlers support to Agentops

Changes Summary

• Classified the LangChain callbacks into two classes:
  • LangchainCallbackHandler (sync version)
  • AsyncLangchainCallbackHandler (async version)
• Fixed parent-child relationships between spans by properly passing context

Implementation Details

Trace Hierarchy

The handler properly maintains a hierarchical trace structure:

• Session spans act as the root for all operations
• Chain spans are children of the session or other chain spans
• LLM spans are children of their parent chain spans
• Tool and agent spans maintain proper parent relationships

Delegation Pattern

Instead of duplicating code, the async handler delegates to the sync handler:

• Maintains the same functionality across sync and async callbacks
• Simplifies maintenance as changes only need to be made in one place
• Adds only minimal overhead while ensuring consistent behavior

🧪 Testing
Tested it with langchain example scripts, here are a few results:
Comprehensive Example
Agencyswarm Example

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

📢 Thoughts on this report? Let us know!

[tcdent]

Nice! Looks good to me.

@the-praxs did you get a chance to test this?

[dot-agi]

Haven't tested after the latest commit.

But since you approved it I am happy to approve and get this merged.

[dot-agi]

YOLO