Replace bincode with borsh (#452)

* Add SignalsConfig to chain_spec

* Correct multiexp feature flagging for rand_core std

* Remove bincode for borsh

Replaces a non-canonical encoding with a canonical encoding which additionally
should be faster.

Also fixes an issue where we used bincode in transcripts where it cannot be
trusted.

This ended up fixing a myriad of other bugs observed, unfortunately.
Accordingly, it either has to be merged or the bug fixes from it must be ported
to a new PR.

* Make serde optional, minimize usage

* Make borsh an optional dependency of substrate/ crates

* Remove unused dependencies

* Use [u8; 64] where possible in the processor messages

* Correct borsh feature flagging

substrate/client/tests/validator_sets.rs

@@ -5,7 +5,7 @@ use sp_core::{sr25519::Public, Pair};
 use serai_client::{
   primitives::{NETWORKS, NetworkId, insecure_pair_from_name},
   validator_sets::{
-    primitives::{Session, ValidatorSet, musig_key},
+    primitives::{Session, ValidatorSet, KeyPair, musig_key},
     ValidatorSetsEvent,
   },
   Serai,
@@ -28,7 +28,7 @@ serai_test!(
     OsRng.fill_bytes(&mut ristretto_key);
     let mut external_key = vec![0; 33];
     OsRng.fill_bytes(&mut external_key);
-    let key_pair = (Public(ristretto_key), external_key.try_into().unwrap());
+    let key_pair = KeyPair(Public(ristretto_key), external_key.try_into().unwrap());
 
     // Make sure the genesis is as expected
     assert_eq!(