feat: Working VoIP calling implementation (Flutter + Android)

Working video and audio calls, as well as android integration

test/liblinphone_flutter_method_channel_test.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:liblinphone_flutter/liblinphone_flutter_method_channel.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  MethodChannelLiblinphoneFlutter platform = MethodChannelLiblinphoneFlutter();
+  const MethodChannel channel = MethodChannel('liblinphone_flutter');
+
+  setUp(() {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
+      channel,
+      (MethodCall methodCall) async {
+        return '42';
+      },
+    );
+  });
+
+  tearDown(() {
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(channel, null);
+  });
+
+  test('getPlatformVersion', () async {
+    expect(await platform.getPlatformVersion(), '42');
+  });
+}