States.serialize_json() missing MKSKIPPED field in serialized output

[PromiseFru]

The States.serialize_json() method does not include the MKSKIPPED field in the serialized JSON output, but States.deserialize_json() expects this field to be present, causing deserialization to fail with a KeyError.

KeyError: 'MKSKIPPED'  File "smswithoutborders_libsig/protocols.py", line 156,
in deserialize_json  for key_str, mk_value_encoded in
state_dict["MKSKIPPED"].items():  ~~~~~~~~~~^^^^^^^^^^^^^