fix: clean up after trajectory rollout

[rasdani]

Description

otherwise delete_sandbox and hence my overridden post_rollout wouldn't be called.

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
• [ ] Test improvement

Testing

• [ ] All existing tests pass when running uv run pytest locally.
• [ ] New tests have been added to cover the changes

Checklist

• [ ] My code follows the style guidelines of this project as outlined in AGENTS.md
• [ ] 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
• [ ] My changes generate no new warnings
• [ ] Any dependent changes have been merged and published

Additional Notes

[CLAassistant]

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1 out of 2 committers have signed the CLA.

:white_check_mark: willccbb
:x: rasdani
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