bug: more gracefully handle run not found in langchain python

[marcklingen]

Describe the bug

Currently the run_id needs to be available while the callback handler is executed. This works fine when the callbackhandler is passed to invoke/call/stream/... methods.

However, if the callback handler is passed in the constructor of a chain/agent this does not work consistently and leads to Parent run not found / Run not found errors.

To reproduce

Bug reports

• bug: Parent run not found when using Callbacks with langchain EnsembleRetriever #1818

Additional information

No response