refactor: use QPurchaseResult instead of QDeferredTransaction for deferred purchases

The Sandwich bridge emits a PurchaseResult map (not a flat
DeferredTransaction). Reuse the existing QPurchaseResult model
for the deferredPurchaseStream, matching the native SDK interface.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: NickSxti

lib/qonversion_flutter.dart

@@ -1,5 +1,4 @@
 export 'src/dto/attribution_provider.dart';
-export 'src/dto/deferred_transaction.dart';
 export 'src/dto/eligibility.dart';
 export 'src/dto/entitlement.dart';
 export 'src/dto/entitlement_grant_type.dart';

lib/src/dto/deferred_transaction.dart

@@ -59,13 +59,13 @@ class QonversionInternal implements Qonversion {
       });
 
   @override
-  Stream<QDeferredTransaction> get deferredPurchaseStream =>
+  Stream<QPurchaseResult> get deferredPurchaseStream =>
       _deferredPurchaseEventChannel
           .receiveBroadcastStream()
           .cast<String>()
           .map((event) {
         final Map<String, dynamic> decodedEvent = jsonDecode(event);
-        return QDeferredTransaction.fromJson(decodedEvent);
+        return QPurchaseResult.fromJson(decodedEvent);
       });
 
   @override

lib/src/internal/qonversion_internal.dart

@@ -41,8 +41,8 @@ abstract class Qonversion {
 
   /// Yields an event each time a deferred purchase completes.
   /// For example, when pending purchases like SCA, Ask to Buy, etc., are approved.
-  /// Provides full transaction details, including for consumable products without entitlements.
-  Stream<QDeferredTransaction> get deferredPurchaseStream;
+  /// Provides the full purchase result with entitlements and store transaction details.
+  Stream<QPurchaseResult> get deferredPurchaseStream;
 
   /// Yields an event each time a promo transaction happens on iOS.
   /// Returns App Store product ID