feat(miniprotocols): Implement tx submission client (#220)

* feat(miniprotocols): Implement tx submission client

* Match CDDL specs

* Fix build errors

* Add server implementation for txsubmission

Also includes some documentation for how to use both the client and the server

* cargo fmt

* clippy suggestions

clippy pls

* Fail explicitly on missing n2c unix socket

---------

Co-authored-by: Pi Lanningham <pi@sundaeswap.finance>

pallas-multiplexer/README.md

@@ -64,7 +64,7 @@ thread::spawn(move || {
     // whatever get received for this mini-protocol.
     loop {
         let payload = rx.recv().unwrap();
-        println!("id:{}, length:{}", protocol, payload.len());
+        println!("id:{protocol}, length:{}", payload.len());
     }
 });
 ```