Create dedicated message structures for FROST messages (#140)

* Create message types for FROST key gen

Taking in reader borrows absolutely wasn't feasible. Now, proper types
which can be read (and then passed directly, without a mutable borrow)
exist for key_gen. sign coming next.

* Move FROST signing to messages, not Readers/Writers/Vec<u8>

Also takes the nonce handling code and makes a dedicated file for it, 
aiming to resolve complex types and make the code more legible by 
replacing its previously inlined state.

* clippy

* Update FROST tests

* read_signature_share

* Update the Monero library to the new FROST packages

* Update processor to latest FROST

* Tweaks to terminology and documentation

processor/src/tests/mod.rs

@@ -1,5 +1,4 @@
 use std::{
-  io::Cursor,
   sync::{Arc, RwLock},
   collections::HashMap,
 };
@@ -19,7 +18,7 @@ struct LocalNetwork {
   i: u16,
   size: u16,
   round: usize,
-  rounds: Arc<RwLock<Vec<HashMap<u16, Cursor<Vec<u8>>>>>>,
+  rounds: Arc<RwLock<Vec<HashMap<u16, Vec<u8>>>>>,
 }
 
 impl LocalNetwork {
@@ -35,13 +34,13 @@ impl LocalNetwork {
 
 #[async_trait]
 impl Network for LocalNetwork {
-  async fn round(&mut self, data: Vec<u8>) -> Result<HashMap<u16, Cursor<Vec<u8>>>, NetworkError> {
+  async fn round(&mut self, data: Vec<u8>) -> Result<HashMap<u16, Vec<u8>>, NetworkError> {
     {
       let mut rounds = self.rounds.write().unwrap();
       if rounds.len() == self.round {
         rounds.push(HashMap::new());
       }
-      rounds[self.round].insert(self.i, Cursor::new(data));
+      rounds[self.round].insert(self.i, data);
     }
 
     while {