Add a test to the coordinator for running a Tributary

Impls a LocalP2p for testing.

Moves rebroadcasting into Tendermint, since it's what knows if a message is
fully valid + original.

Removes TributarySpec::validators() HashMap, as its non-determinism caused
different instances to have different round robin schedules. It was already
prior moved to a Vec for this issue, so I'm unsure why this remnant existed.

Also renames the GH no-std workflow from the prior commit.

coordinator/src/main.rs

@@ -94,7 +94,7 @@ async fn main() {
   let db = MemDb::new(); // TODO
 
   let key = Zeroizing::new(<Ristretto as Ciphersuite>::F::ZERO); // TODO
-  let p2p = LocalP2p {}; // TODO
+  let p2p = LocalP2p::new(1).swap_remove(0); // TODO
 
   let processor = processor::MemProcessor::new(); // TODO