Function handle_incoming_packet 

async fn handle_incoming_packet<R, W>(
    header_result: Result<FixedHeader, Error>,
    io: &mut PacketIo<'_, R, W>,
    keep_alive_timer: &mut Pin<&mut Sleep>,
) -> Option<DisconnectReason>
where
    R: AsyncReadExt + Unpin,
    W: AsyncWrite + Unpin,