feat(tool-calling): add tool call passthrough support in LLMRails

[Pouyanpi]

This PR implements tool call extraction and passthrough functionality in LLMRails, enabling the framework to capture and forward tool calls from LLM responses. Key changes include:

• Add tool_calls_var context variable for storing LLM tool calls
• Refactor llm_call utils to extract and store tool calls from responses
• Support tool calls in both GenerationResponse and dict message formats
• Add ToolMessage support for langchain message conversion
• Comprehensive test coverage for tool calling integration scenarios

The implementation maintains backward compatibility while adding new tool calling capabilities to the passthrough mode.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.73%. Comparing base (eb29437) to head (8902ddb).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1364      +/-   ##
===========================================
+ Coverage    71.66%   71.73%   +0.07%     
===========================================
  Files          171      171              
  Lines        17015    17045      +30     
===========================================
+ Hits         12193    12227      +34     
+ Misses        4822     4818       -4     

Flag	Coverage Δ
python	71.73% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
nemoguardrails/actions/llm/utils.py	82.31% <100.00%> (+2.31%)	⬆️
nemoguardrails/context.py	100.00% <100.00%> (ø)
nemoguardrails/rails/llm/llmrails.py	90.52% <100.00%> (+0.06%)	⬆️
nemoguardrails/rails/llm/options.py	63.39% <100.00%> (+0.32%)	⬆️

... and 1 file with indirect coverage changes

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[github-actions]

Documentation preview

https://nvidia.github.io/NeMo-Guardrails/review/pr-1364

[tgasser-nv]

Looks good, left some comments to address before merging. This is a huge PR (4k LOC) could you split this type of change into multiple smaller PRs in future?

Also could you add some local integration testing to check this works when interfacing with real Nemoguard / LLMs which support tool-calling?

[Pouyanpi]

Looks good, left some comments to address before merging. This is a huge PR (4k LOC) could you split this type of change into multiple smaller PRs in future?

Also could you add some local integration testing to check this works when interfacing with real Nemoguard / LLMs which support tool-calling?

You are absolutely right, sorry for that. I can see that commits of another PR has gotten here probably during rebase.

Now it is around 890

[codecov-commenter]

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