fix: resolve slow exit and reduce test timeouts (#1970)

- Explicitly shutdown tokio runtime on launcher cleanup to fix slow exit
- Add timeout to tunnel connector in tests to prevent hanging
- Reduce test wait durations from 5s to 100ms for faster test execution
- Bump num-bigint-dig from 0.8.4 to 0.8.6

easytier/src/launcher.rs

@@ -241,6 +241,7 @@ impl EasyTierLauncher {
             }
             instance_alive.store(false, std::sync::atomic::Ordering::Relaxed);
             notifier.notify_one();
+            rt.shutdown_background();
         }));
     }