refactored langchain integration and tutorial

[vaahtio]

LangChain Integration for Flow Judge

Summary

This PR introduces an integration between Flow Judge and LangChain, allowing users to leverage Flow Judge's custom metrics within LangChain workflows.

Key Changes

1. Created FlowJudgeLangChainEvaluator class on the integrations folder:

   • Extends LangChain's StringEvaluator
   • Enables use of Flow Judge metrics in LangChain pipelines
   • Refactored to the changes in main branch mainly related to model classes

2. Added example notebook:

   • Demonstrates usage of Flow Judge integration within LangChain
   • Compares Flow Judge custom metrics with LangChain's built-in QA evaluator

Testing

The integration has been manually tested:

• On linux Ubuntu 22.04.3 LTS
• Verified functionality of FlowJudgeLangChainEvaluator with models Flow-Judge-v0.1-AWQ, Flow-Judge-v0.1, Flow-Judge-v0.1_HF and Flow-Judge-v0.1-AWQ-Async ( note Async functionality is not demonstrated in the notebook, but it was part of the standard stringevaluator class, so I added the option as well)
• Verified functionality of FlowJudgeLangChainEvaluator with custom metric (in notebook), and built-in metrics (metric=RESPONSE_CORRECTNESS_BINARY, model=model)
• Tested integration in example notebook, ensuring correct behaviour within LangChain workflows
• Manually viewed results with LangChain's native evaluators to confirm accuracy and consistency

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 51 lines in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
flow_judge/integrations/langchain.py	0.00%	51 Missing :warning:

Files with missing lines	Coverage Δ
flow_judge/integrations/langchain.py	0.00% <0.00%> (ø)

... and 9 files with indirect coverage changes