feat: switch iperf3 to JNI with 3.19 source

- Switch from bundled iperf3 binary (Process.start) to JNI compilation
- iperf3 3.21 source API was incompatible (start_time, iperf_strerror, etc.)
- iperf3 3.19 source is proven to work (used by CellularLab)
- CMakeLists.txt updated: config.h generated into cpp/iperf/ for correct include paths
- iperf_jni.c fixed for 3.19 API (no start_time on iperf_test)
- getTestProgress() returns g_test->duration as fallback (no real-time elapsed tracking yet)
- NDK CMake pinned to 3.22.1
- UI layer updated: removed Iperf3BinaryPathProvider references
- Tests updated: TestRunViewModelTest matches new service interface
- pubspec.yaml: removed iperf3 assets bundle, added http dependency
- AndroidManifest: INTERNET permission (needed for hostname resolution)

lib/data/services/iperf3_binary_path_provider.dart

@@ -1,58 +1,9 @@
-import 'dart:io';
+// This file is kept as a stub — iperf3 is now compiled as a native
+// shared library (libiperf3jni.so) via JNI.
+// The old binary-path-provider pattern (extract ELF from assets → chmod → execve)
+// was replaced by the JNI approach after SELinux blocked binary execution.
+// See .hermes/plans/ for details on the migration.
 
-import 'package:flutter/services.dart';
-import 'package:path_provider/path_provider.dart';
-
-/// Provides the path to the iperf3 binary on the device.
-///
-/// Call [initialize] in [main] (before [runApp]) to extract the
-/// bundled asset and populate the cache. After initialization,
-/// [path] returns a synchronous [String].
-class Iperf3BinaryPathProvider {
-  static String? _cachedPath;
-
-  /// Extract the bundled iperf3 binary to the app's cache directory.
-  ///
-  /// Call this once in [main] before [runApp].
-  static Future<void> initialize() async {
-    if (_cachedPath != null) return;
-
-    final cacheDir = await getApplicationCacheDirectory();
-    final binaryDir = Directory('${cacheDir.path}/iperf3');
-    if (!await binaryDir.exists()) {
-      await binaryDir.create(recursive: true);
-    }
-
-    final abi = await _detectAbi();
-    final assetPath = 'assets/iperf3/$abi/iperf3';
-
-    final bytes = await rootBundle.load(assetPath);
-    final file = File('${binaryDir.path}/iperf3');
-    await file.writeAsBytes(bytes.buffer.asUint8List());
-
-    // chmod +x the binary — /system/bin/sh is always present on Android
-    await Process.run(
-      '/system/bin/sh',
-      ['-c', 'chmod +x "\$1"', '_', file.path],
-    );
-
-    _cachedPath = file.path;
-  }
-
-  /// The resolved path to the iperf3 binary.
-  ///
-  /// Must call [initialize] first, or this will return a placeholder.
-  static String get path {
-    return _cachedPath ?? '/data/local/tmp/iperf3';
-  }
-
-  static Future<String> _detectAbi() async {
-    final result = await Process.run(
-      'getprop',
-      ['ro.product.cpu.abi'],
-    );
-    final abi = result.stdout.toString().trim();
-    if (abi.contains('arm64')) return 'arm64-v8a';
-    return 'armeabi-v7a';
-  }
-}
+// The Iperf3Service now uses MethodChannel to communicate with Kotlin/JNI:
+//   Dart → MethodChannel → Kotlin → JNI → iperf3 (same process)
+// No file extraction, no chmod, no Process.start needed.