`segy_to_mdio` and `mdio_to_segy` do not have uniform behavior for text header handling

[BrianMichell]

An EBCIDIC header may look like this when ingested with segy_to_mdio. This will not export symmetrically from mdio_to_segy.

�C38 �C39 �C
40 END EBCDIC

We should either reject the ingestion, make the correction during ingestion, or make the correction during export with a logging.warning.

[BrianMichell]

After some end-user discussion we will update MDIO__IMPORT__SAVE_SEGY_FILE_HEADER env var behavior.

1. Update from type bool to int.
2. Restrict values to 0 1 2.
3. Maintain backwards compatibility.

0/False: Same behavior -- Do not save segy file header
1/True: Save segy file header but raise error on malformed text header.
2: Save segy file header and make corrections.

• Unserializable characters converted to spaces
• Pad text header to 80*40 characters.