feat(ads): add AdFeedItem class for native ads integration

- Create AdFeedItem class to wrap loaded native ad objects
- Implement EquatableMixin for easy comparison
- Add properties for unique identifier and native ad object
- Enable seamless integration of ads into the application's feed structure

Author: fulleni

lib/ads/models/ad_feed_item.dart

@@ -0,0 +1,32 @@
+import 'package:core/core.dart';
+import 'package:equatable/equatable.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart';
+
+/// {@template ad_feed_item}
+/// A [FeedItem] that wraps a loaded native ad object from an ad network SDK.
+///
+/// This class allows actual, displayable ad objects (like [NativeAd] from
+/// Google Mobile Ads) to be seamlessly integrated into the application's
+/// generic feed structure alongside other content types (e.g., [Headline]).
+/// {@endtemplate}
+class AdFeedItem extends FeedItem with EquatableMixin {
+  /// {@macro ad_feed_item}
+  const AdFeedItem({
+    required this.id,
+    required this.nativeAd,
+  }) : super(type: 'ad_feed_item');
+
+  /// A unique identifier for this specific ad instance in the feed.
+  ///
+  /// This is distinct from the ad unit ID and is used for tracking
+  /// the ad within the feed.
+  final String id;
+
+  /// The loaded native ad object from the ad network SDK.
+  ///
+  /// This object contains the actual ad content and is ready for display.
+  final NativeAd nativeAd;
+
+  @override
+  List<Object?> get props => [id, nativeAd, type];
+}