Add server/client handshake

[chipsenkbeil]

We need this for a couple of reasons:

1. Provide the client the ability to pick the compression and encryption it wants to use from those made available by the server. Upon receiving a selection, the server would generate the appropriate codecs to support this.
2. Replay missed messages similar to Eternal Terminal's backed reader and writer. On handshake, the client and server would send each other any missed messages

For the first reason, we may want to implement discriminants for CompressionCodec and possibly merge PlainCodec and XChaCha20Poly1305 into EncryptionCodec so we can do the same for it. We'd have a serializable struct that has an Option<CompressionType> and EncryptionType. Additionally, this would include a ClientId or something similar that can be used to determine if replaying is necessary along with the SeqCnt to indicate how far along it is.

The server would send the options, and the client would respond with its selection.

The server would have a new, required (?) method:

async fn on_handshake(&self, transport: FramedTransport<T, ()>) -> io::Result<FramedTransport<T, Box<dyn Codec>>> {
    // NOTE: Need a way to map the codec of a transport -- should be pretty easy to do since we can consume the transport
    Ok(transport)
}

T is a generic for the underlying transport and () would be our default codec that has no encryption or compression.

[chipsenkbeil]

Now implemented in branch using Connection<T> to facilitate the client/server handshake, ability for client to reconnect, and backup restoration.

Handshake includes establishment of codec, authentication, and backup restoration.

[github-actions]

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