test(cli): add comprehensive tests for multi-target resolution and output

Add unit tests for target normalization and address family filtering, and expand integration tests to verify column rendering and CSV output for multiple targets. Update subscriber config to drop oldest events under backpressure for better CLI stability.

crates/irtt-cli/src/cmd/client/run.rs

@@ -285,7 +285,11 @@ fn run_group_stream(
         managed_targets,
         SubscriberConfig {
             capacity: 16_384,
-            overflow: SubscriberOverflow::Disconnect,
+            // CLI output is best-effort under sustained backpressure. Dropping
+            // stale rows keeps continuous runs attached to the running group
+            // instead of turning a full output queue into a disconnected
+            // subscriber and a potentially blocking join.
+            overflow: SubscriberOverflow::DropOldest,
         },
     )?;