feat(ads): implement native ad feed item widget

Create a new widget for displaying native ads within the feed. This widget:
- Takes an AdFeedItem and renders it using AdWidget.
- Handles the disposal of the NativeAd to prevent memory leaks.
- Shows an empty container if the ad is not loaded.

This change allows for better integration of native ads within the app's content feed.

Author: fulleni

lib/shared/widgets/ads/ad_feed_item_widget.dart

@@ -0,0 +1,65 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/ad_feed_item.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart';
+import 'package:ui_kit/ui_kit.dart';
+
+/// {@template ad_feed_item_widget}
+/// A widget responsible for rendering a native ad within the feed.
+///
+/// This widget takes an [AdFeedItem] and uses the `AdWidget` from the
+/// `google_mobile_ads` package to display the underlying [NativeAd].
+/// It also handles the disposal of the ad object to prevent memory leaks.
+/// {@endtemplate}
+class AdFeedItemWidget extends StatefulWidget {
+  /// {@macro ad_feed_item_widget}
+  const AdFeedItemWidget({required this.adFeedItem, super.key});
+
+  /// The ad feed item containing the loaded native ad to be displayed.
+  final AdFeedItem adFeedItem;
+
+  @override
+  State<AdFeedItemWidget> createState() => _AdFeedItemWidgetState();
+}
+
+class _AdFeedItemWidgetState extends State<AdFeedItemWidget> {
+  NativeAd? _nativeAd;
+  bool _isAdLoaded = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _nativeAd = widget.adFeedItem.nativeAd;
+    // The ad is typically already loaded by the AdService before being passed here.
+    // We can set the state to reflect this.
+    if (_nativeAd != null) {
+      _isAdLoaded = true;
+    }
+  }
+
+  @override
+  void dispose() {
+    // Dispose the native ad when the widget is removed from the tree.
+    _nativeAd?.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final nativeAd = _nativeAd;
+    if (!_isAdLoaded || nativeAd == null) {
+      // If the ad is not loaded for any reason, return an empty container.
+      return const SizedBox.shrink();
+    }
+
+    return Card(
+      margin: const EdgeInsets.symmetric(
+        vertical: AppSpacing.sm,
+        horizontal: AppSpacing.lg,
+      ),
+      child: SizedBox(
+        height: 120,
+        child: AdWidget(ad: nativeAd),
+      ),
+    );
+  }
+}