feat: 支付验签框架 — 策略模式 + 装饰器重试

- 新增 IPaymentVerifier 接口 (Verify + Consume)，渠道无关
- 新增 PaymentVerifierFactory 按 Channel 分发
- 新增 FlexionPaymentVerifier: HTTP 验签 + 线性 backoff 重试
- 新增 DummyPaymentVerifier: 占位验签实现
- 新增 RetryablePaymentVerifier: 装饰器，流程级重试
- TYSdkFacade_Pay: PayResult 增加验签分支，先验签后消费再回调
- TYSdkModel: PaymentInfo 增加 verified 字段
- UnityBridgeFunc: 移除 ConsumeFlexionPurchase（职责收归 Verifier）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

sdk-intergration/Packages/tysdk/Runtime/TYSdkFacade_Pay.cs

@@ -128,7 +128,47 @@ namespace tysdk
                 }
                 return;
             }
-            TYSDKCallbackManager.Instance.TryTriggerCallback(result);
+            var verifier = PaymentVerifierFactory.GetVerifier();
+            if (verifier != null && !string.IsNullOrEmpty(result.purchaseJson))
+            {
+                _VerifyPurchase(result, verifier);
+            }
+            else
+            {
+                TYSDKCallbackManager.Instance.TryTriggerCallback(result);
+            }
+        }
+
+        private async void _VerifyPurchase(PaymentInfo result, IPaymentVerifier verifier)
+        {
+            TYSDKCallbackManager.Instance.ResetCallbackTimeout<PaymentInfo>(TimeSpan.FromSeconds(60));
+            try
+            {
+                var verifyResult = await verifier.Verify(result);
+                if (verifyResult.success)
+                {
+                    result.verified = true;
+                    if (!string.IsNullOrEmpty(result.purchaseToken))
+                    {
+                        verifier.Consume(result.purchaseToken);
+                    }
+                    TYSDKCallbackManager.Instance.TryTriggerCallback(result);
+                }
+                else
+                {
+                    Debug.LogWarning("[TYSdkFacade] Payment verification failed: " + verifyResult.msg);
+                    result.code = "-1";
+                    result.msg = "verification_failed: " + verifyResult.msg;
+                    TYSDKCallbackManager.Instance.TryTriggerCallback(result);
+                }
+            }
+            catch (Exception e)
+            {
+                Debug.LogError("[TYSdkFacade] Verification exception: " + e.Message);
+                result.code = "-1";
+                result.msg = "verification_error: " + e.Message;
+                TYSDKCallbackManager.Instance.TryTriggerCallback(result);
+            }
         }
 
         public async Task<ProductListInfo> GetSKUList()