Remove RawPacket and use slice instead

[akumaigorodski]

Here's my issue with RawPacket in the following example:

if let Some((Ok(raw_packet), _)) = parser.push_bytes_raw(out_buffer) {
    if let Ok(Packet::RcChannelsPacked(rc)) = Packet::parse(raw_packet) { // RawPacket gets moved here
        // we got specifically RC packet, do stuff
    }
    
    // forward RawPacket to flight controller anyway, whatever it happens to be
    // but we can not because it has been moved
    fc_port.write(raw_packet)
}

So, why don't we just drop it altogether and work with slices everywhere? In that case the code above just works without any changes. We will only lose a bit of semantic meaning, but arguably not much.

[tact1m4n3]

The good thing with RawPacket is it guarantees that the packet is valid (it can only be created by a parser). I don't really like using a slice instead. We could #[derive(Clone, Copy)] the RawPacket as an alternative.