Add support for tracking base LangChain Runnables in callback handler

[dnandakumar-nv]

Is this a new feature, an improvement, or a change to existing functionality?

New Feature

How would you describe the priority of this feature request

Critical (currently preventing usage)

Please provide a clear description of problem this feature solves

I want NAT to be able to also instrument base Runnable invocations from LangChain in the callback handler. Currently, the handler tracks tool start, tool end, llm start, llm end, and chat model events. This assumes that the LangChain class is a subtype of class Runnable that invokes type specific callback methods.

The callback handler will need to be extended with on_chain_start and on_chain_end events to be able to also track Runnable invocations.

Describe your ideal solution

Transparent instrumentation of runnable classes with the relevant callback methods.

Additional context

No response

Code of Conduct

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• I have searched the open feature requests and have found no duplicates for this feature request