feat: add domain models for test configuration and results

lib/domain/models/iperf3_result.dart

@@ -0,0 +1,10 @@
+/// Raw result from an iperf3 execution.
+class Iperf3Result {
+  final String rawOutput;
+  final int exitCode;
+
+  const Iperf3Result({
+    required this.rawOutput,
+    required this.exitCode,
+  });
+}

lib/domain/models/test_configuration.dart

@@ -0,0 +1,37 @@
+/// Configuration for an iperf3 client test.
+class TestConfiguration {
+  final String server;
+  final int port;
+  final Duration duration;
+  final int interval;
+  final int parallelStreams;
+
+  const TestConfiguration({
+    this.server = 'iperf.es.net',
+    this.port = 5201,
+    this.duration = const Duration(seconds: 10),
+    this.interval = 1,
+    this.parallelStreams = 1,
+  });
+
+  /// Convert to iperf3 CLI arguments.
+  List<String> toCliArgs() {
+    return <String>[
+      '-c', server,
+      '-p', '$port',
+      '-t', '${duration.inSeconds}',
+      '-i', '$interval',
+      '-P', '$parallelStreams',
+    ];
+  }
+
+  /// Validate the configuration.
+  bool get isValid {
+    if (server.isEmpty) return false;
+    if (port < 1 || port > 65535) return false;
+    if (duration.inSeconds < 1) return false;
+    if (interval < 1) return false;
+    if (parallelStreams < 1) return false;
+    return true;
+  }
+}