Add a UID function to messages

When we receive messages, we're provided with a message ID we can use to
prevent handling an item multiple times. That doesn't prevent us from *sending*
an item multiple times though. Thanks to the UID system, we can now not send if
already present.

Alternatively, we can remove the ordered message ID for just the UID, allowing
duplicates to be sent without issue, and handled on the receiving end.

processor/src/main.rs

@@ -383,6 +383,7 @@ async fn handle_coordinator_msg<D: Db, C: Coin, Co: Coordinator>(
 
         messages::substrate::CoordinatorMessage::SubstrateBlock {
           context,
+          network,
           block,
           key: key_vec,
           burns,
@@ -408,7 +409,11 @@ async fn handle_coordinator_msg<D: Db, C: Coin, Co: Coordinator>(
               instruction: OutInstruction { address, data },
               balance,
             } = out;
+            // TODO: Check network is this coin's network
+            assert_eq!(balance.coin.network(), network);
+
             if let Ok(address) = C::Address::try_from(address.consume()) {
+              // TODO: Add coin to payment
               payments.push(Payment {
                 address,
                 data: data.map(|data| data.consume()),
@@ -426,6 +431,7 @@ async fn handle_coordinator_msg<D: Db, C: Coin, Co: Coordinator>(
           coordinator
             .send(ProcessorMessage::Coordinator(
               messages::coordinator::ProcessorMessage::SubstrateBlockAck {
+                network,
                 block,
                 plans: plans.iter().map(|plan| plan.id()).collect(),
               },