feat: add response format handling in judge rubric

[lakshyaag]

Description

From #331 This PR adds response_format to the default judge rubric parameters. On specifying a OpenAI-compatible ResponseFormat, the request will use the .parse() method in the OpenAI SDK.

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update
• [ ] Test improvement

Testing

• [x] All existing tests pass
• [x] New tests have been added to cover the changes
• [x] Tests have been run locally with uv run pytest

Test Coverage

• Current coverage: ___%
• Coverage after changes: ___%

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] Any dependent changes have been merged and published

Additional Notes

[wcummings]

It would also be nice to be able to use response_format/structured responses in the user_client, or is this better handled with tool calling?

[willccbb]

@lakshyaag Can this not already be done by passing response_format via sampling_args? Would rather have that be the all-in-one route for expressing additional configurations rather than explicitly adding each one.

[lakshyaag]

@willccbb I'll look into it - should be able to support it.

[lakshyaag]

@cursoragent look into it