tor-circmgr: impl Display for TargetPort

This will be used for error handling, and perhaps other things.

crates/tor-circmgr/src/usage.rs

@@ -2,6 +2,7 @@
 
 use rand::Rng;
 use serde::{Deserialize, Serialize};
+use std::fmt::{self, Display};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
 use tracing::debug;
@@ -59,6 +60,12 @@ impl TargetPort {
     }
 }
 
+impl Display for TargetPort {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}{}", self.port, if self.ipv6 { "v6" } else { "v4" })
+    }
+}
+
 /// A token used to isolate unrelated streams on different circuits.
 ///
 /// When two streams are associated with different isolation tokens, they