Remove coin crate

Effective reversion of past few commits by request.

processor/src/lib.rs

@@ -3,10 +3,10 @@ use std::{marker::Send, io::Cursor, collections::HashMap};
 use async_trait::async_trait;
 use thiserror::Error;
 
-use frost::FrostError;
+use frost::{curve::Curve, FrostError};
 
-pub use serai_coin as coin;
-use coin::CoinError;
+mod coin;
+use coin::{CoinError, Coin};
 
 mod wallet;
 
@@ -30,3 +30,11 @@ pub enum SignError {
   #[error("network had an error {0}")]
   NetworkError(NetworkError),
 }
+
+// Generate a static additional key for a given chain in a globally consistent manner
+// Doesn't consider the current group key to increase the simplicity of verifying Serai's status
+// Takes an index, k, to support protocols which use multiple secondary keys
+// Presumably a view key
+pub(crate) fn additional_key<C: Coin>(k: u64) -> <C::Curve as Curve>::F {
+  C::Curve::hash_to_F(b"Serai DEX Additional Key", &[C::ID, &k.to_le_bytes()].concat())
+}