Function make_talker_alias 

fn make_talker_alias(callsign: &str, suffix: Option<&str>) -> String

Builds the talkerAlias field from a callsign and optional suffix.

("W1AW", Some("D75")) → "W1AW / D75", ("W1AW", None) → "W1AW". Trims trailing whitespace from the suffix because D-STAR pads suffixes to 4 bytes on the wire.