Refactor metrics and imports across multiple files
- Removed unused import of CORE_LABELS in metrics.py.
- Updated import statements in api.py for consistency.
- Cleaned up import order in worker.py for better readability.
- Added missing newline at the end of metrics.py.
- Adjusted formatting in core_scouter.py to ensure proper syntax.
- Removed redundant 'on_conflict' and 'unique_columns' keys from test cases in test_core_scouter.py for clarity.
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