A plain NamedTemporaryFile is sufficient here: we only need a single file, not a directory to hold it. Using NamedTemporaryFile is simpler (no subdirectory to manage) and gives us a .json suffix for free, which editors use for syntax highlighting.
filesystem: JsonEditor: offer interactive retry on error
When json.loads() fails (e.g. the user made a syntax mistake), prompt the user with "Re-open file for editing? [y]es/[n]o:" and loop back to the editor if they answer 'y' or 'yes'. If the user declines, return the original unmodified value so no write is attempted; the temp file is still cleaned up by __exit__() in that case.
tests: fix TransRecEF _test_de_encode to operate at file level
Previously, _test_de_encode vectors for TransRecEF subclasses were tested via decode_record_hex()/encode_record_hex(), i.e. one record at a time, with the decoded value being a scalar.
Switch test_de_encode_record() in TransRecEF_Test to use decode_hex() / encode_hex() instead, so that vectors represent whole-file content (decoded value is a list of records) -- consistent with how LinFixedEF handles _test_de_encode. Update all existing vectors accordingly.
