Function parse_channel_modes 

pub fn parse_channel_modes(
    isupport: &Isupport,
    params: &[String],
) -> Vec<ModeChange>

Split a channel MODE change into one entry per letter.

params is everything after the target: the mode string, then its arguments.

A letter the server never advertised is treated as taking no argument. Consuming one instead would shift every following argument onto the wrong letter, and a missing argument is the cheaper mistake to recover from.