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

tests/processor/src/lib.rs

@@ -224,7 +224,7 @@ impl Coordinator {
           to: Service::Processor(self.network),
           intent: msg.intent(),
         },
-        serde_json::to_string(&msg).unwrap().into_bytes(),
+        borsh::to_vec(&msg).unwrap(),
       )
       .await;
     self.next_send_id += 1;
@@ -242,7 +242,7 @@ impl Coordinator {
     assert_eq!(msg.id, self.next_recv_id);
     self.queue.ack(Service::Processor(self.network), msg.id).await;
     self.next_recv_id += 1;
-    serde_json::from_slice(&msg.msg).unwrap()
+    borsh::from_slice(&msg.msg).unwrap()
   }
 
   pub async fn add_block(&self, ops: &DockerOperations) -> ([u8; 32], Vec<u8>) {