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.
