🧹 Remove unused json import in test_calibration.py

[manupawickramasinghe]

🎯 What: Removed the unused import json from aether-arena/calibration/test_calibration.py.
💡 Why: json was imported but never utilized in the script. Removing it improves code clarity, eliminates an unnecessary linter warning, and marginally reduces overhead.
✅ Verification: Verified with flake8 to ensure the file linting passes (except for pre-existing line length issues) and successfully executed the test suite in aether-arena/calibration/ using pytest -c /dev/null with no regressions.
✨ Result: Cleaned up code dependencies without changing functionality.

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PR created automatically by Jules for task 6587464740656360351 started by @manupawickramasinghe

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