Handle removing a node, and a shard disconnecting (bulk remove)

backend/common/src/assign_id.rs

@@ -1,4 +1,4 @@
-use std::hash::Hash;
+use std::{fmt::Display, hash::Hash};
 use serde::{Serialize,Deserialize};
 use bimap::BiMap;
 
@@ -15,6 +15,11 @@ impl std::convert::From<usize> for Id {
         Id(n)
     }
 }
+impl Display for Id {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
+}
 
 /// A struct that allows you to assign an ID to an arbitrary set of
 /// details (so long as they are Eq+Hash+Clone), and then access