feat: add payment

lib/core/payment/myket_payment_gateway.dart

@@ -0,0 +1,40 @@
+import 'package:myket_iap/myket_iap.dart';
+import 'package:myket_iap/util/purchase.dart';
+
+import '../config.dart';
+import 'payment_gateway.dart';
+
+/// پرداختِ درون‌برنامه‌ایِ مایکت (flavorِ `myket`).
+class MyketPaymentGateway implements PaymentGateway {
+  bool _inited = false;
+
+  @override
+  String get store => 'myket';
+
+  @override
+  Future<void> connect() async {
+    if (_inited) return;
+    await MyketIAP.init(rsaKey: AppConfig.myketRsaKey, enableDebugLogging: false);
+    _inited = true;
+  }
+
+  @override
+  Future<PurchaseResult> purchase(String productSku) async {
+    await connect();
+    final Map<dynamic, dynamic> result =
+        await MyketIAP.launchPurchaseFlow(sku: productSku, payload: 'hakemsho');
+
+    final Purchase? purchase = result[MyketIAP.PURCHASE] as Purchase?;
+    if (purchase == null || purchase.mToken.isEmpty) {
+      return const PurchaseResult.failure();
+    }
+
+    return PurchaseResult.success(
+      token: purchase.mToken,
+      purchaseData: purchase.mOriginalJson,
+      signature: purchase.mSignature,
+      // کالای مصرفی (سکه/بلیت) باید مصرف شود تا کاربر بتواند دوباره بخرد.
+      onConfirmed: () => MyketIAP.consume(purchase: purchase),
+    );
+  }
+}