fn parse_rptr_field(field: &str) -> (Option<String>, Option<String>)Expand description
Parses an RPT field (e.g. "REF001 B") into a reflector callsign and
optional module letter.
The field format is: up to 7 characters of callsign (possibly space-padded),
followed by a space and a single module letter (A-Z). Returns (None, None)
if the field is empty or does not contain a recognisable callsign.