Make progres on handling NewSet events

Further bones out the coordinator.

coordinator/src/p2p.rs

@@ -0,0 +1,25 @@
+use core::fmt::Debug;
+
+use async_trait::async_trait;
+
+use tributary::P2p as TributaryP2p;
+
+// TODO
+#[async_trait]
+pub trait P2p: Send + Sync + Clone + Debug + TributaryP2p {}
+
+// TODO
+#[derive(Clone, Debug)]
+pub struct LocalP2p {}
+
+#[async_trait]
+impl TributaryP2p for LocalP2p {
+  async fn broadcast(&self, msg: Vec<u8>) {
+    // TODO
+    todo!()
+  }
+}
+
+// TODO
+#[async_trait]
+impl P2p for LocalP2p {}