Optimize disk writing frequency in serial_logger.py

[google-labs-jules]

Removed the unconditional log.flush() in serial_logger.py per the FIX comment and task instructions, as the flushing is already handled conditionally at the end of the loop, thereby optimizing disk I/O.

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PR created automatically by Jules for task 10259055331594099350 started by @schwehr

[google-labs-jules]

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