Explicitly close logging FileHandler on all exit paths

[Copilot]

push_metrics.py opened a logging.FileHandler at module level but never explicitly closed it — relying silently on atexit/logging.shutdown() to clean up.

Changes

• push_metrics.py: Wrap main() body in try/finally; call logging.shutdown() in the finally clause to explicitly close all log handlers on every exit path (success, early error return, or unhandled exception).

def main() -> int:
    try:
        ...
        return 0
    finally:
        logging.shutdown()

All other open() calls in the codebase already used with statements and required no changes.

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