Tidy up incomplete files

[mdavis-xyz]

When converting DISPATCHLOAD files to parquet, the process often dies due to running out of memory. This can result in an empty 0 byte parquet file, or other partially-written files. Even if the user reruns nemosis, the library sees a file exists, and doesn't check that it's a valid file, so the error isn't picked up until later when we try to read the file.

This can be prevented by wrapping writes like:

try:
    df.write_parquet(path)
except Exception:
    if os.path.exists(path):
        os.remove(path)
    raise

(True of CSV, feather etc)

This can also happen if the process is terminated for some other reason. (e.g. user clicks stop in jupyter.)

[mdavis-xyz]

Hmm, actually for an out of memory error specifically, the process may be killed before python can gracefully throw an exception. But I still think it's worth adding this because some halting conditions may result in corrupt files being cleaned up.