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/common/in_instructions.rs

@@ -10,7 +10,7 @@ use sp_core::Pair;
 
 use serai_client::{
   primitives::{insecure_pair_from_name, BlockHash, NetworkId, Balance, SeraiAddress},
-  validator_sets::primitives::{Session, ValidatorSet},
+  validator_sets::primitives::{Session, ValidatorSet, KeyPair},
   in_instructions::{
     primitives::{Batch, SignedBatch, batch_message, InInstruction, InInstructionWithBalance},
     InInstructionsEvent,
@@ -30,7 +30,7 @@ pub async fn provide_batch(serai: &Serai, batch: Batch) -> [u8; 32] {
   {
     keys
   } else {
-    let keys = (pair.public(), vec![].try_into().unwrap());
+    let keys = KeyPair(pair.public(), vec![].try_into().unwrap());
     set_keys(serai, set, keys.clone()).await;
     keys
   };