Update tool call tests for new functionality

[willccbb]

## Description
This PR updates existing test cases to reflect recent changes in the repository's core functionality, specifically the transition to using built-in tool call support from inference clients instead of previous hand-rolled logic.

The changes address:
*   **Tool Call Handling**: Updating mock clients to properly support `tool_calls` attributes on messages.
*   **Rubric API Changes**: Adding the required `parser` argument to `Rubric.call_reward_func` calls.
*   **Environment Response Format**: Adjusting environment response methods to return lists of messages instead of single dictionaries.

These updates ensure that all tests accurately reflect the current behavior of the system without silencing or removing any test cases.

## Type of Change
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] 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
- [x] Test improvement

## Testing
- [x] All existing tests pass
- [ ] New tests have been added to cover the changes
- [x] Tests have been run locally with `python -m pytest tests/`

### Test Coverage
- Current coverage: Not applicable (no new code, only test updates)
- Coverage after changes: Not applicable (no new code, only test updates)

## 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
- [x] Any dependent changes have been merged and published

## Additional Notes
This PR specifically targets the `tests/` directory as per the task instructions, ensuring no changes were made to the main application code. The goal was to bring failing tests back to a passing state by aligning them with the updated core logic.

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