Closes the current interchange by writing its footer segment.
def create_interchange_footer() -> None: ...
The on_create_interchange_footer method will write any existing segments to the output stream and then generate and write the interchange closing segment (IEA or UNZ). If there is an open transaction set, on_create_interchange_footer will first call create_transaction_footer to close it. If there is an open functional group, on_create_interchange_footer will first call create_functional_group_footer to close it. If there is no interchange open, an exception will be thrown.