Function decode_qos_override_parts 

pub fn decode_qos_override_parts(
    topic: &'static str,
    role: u8,
    policy: u8,
    value: u32,
) -> Option<QoSOverride>

decode_qos_override over loose parts — for the FFI paths, which read the fields out of a #[repr(C)] struct rather than a tuple.