Function generic_nack_sequence_numbers 

pub fn generic_nack_sequence_numbers(
    pid: u16,
    blp: u16,
) -> impl Iterator<Item = u16>

Expands one Generic NACK PID and bitmask into requested RTP sequence numbers.

The PID is yielded first. Each set BLP bit yields PID + bit index + 1 with 16-bit RTP sequence-number rollover.

Reference: https://www.rfc-editor.org/rfc/rfc4585.html#section-6.2.1