feat(ads): implement AdMob native ad widget

- Create AdMobNativeAdWidget to render Google AdMob native ads
- Handle lifecycle management of native ad object
- Display ad using AdMob SDK's AdWidget
- Add type checking for adObject to ensure it's an AdMob NativeAd
- Provide fallback for unloaded or incorrect ad types

Author: fulleni

lib/ads/widgets/admob_native_ad_widget.dart

@@ -0,0 +1,86 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/native_ad.dart'
+    as app_native_ad;
+import 'package:google_mobile_ads/google_mobile_ads.dart' as admob;
+
+/// {@template admob_native_ad_widget}
+/// A widget responsible for rendering a Google AdMob native ad.
+///
+/// This widget takes our generic [app_native_ad.NativeAd] model, extracts
+/// the underlying [admob.NativeAd] object, and uses the AdMob SDK's
+/// [admob.AdWidget] to display it. It also handles the lifecycle
+/// management of the native ad object.
+/// {@endtemplate}
+class AdMobNativeAdWidget extends StatefulWidget {
+  /// {@macro admob_native_ad_widget}
+  const AdMobNativeAdWidget({
+    required this.nativeAd,
+    super.key,
+  });
+
+  /// The generic native ad data containing the AdMob-specific ad object.
+  final app_native_ad.NativeAd nativeAd;
+
+  @override
+  State<AdMobNativeAdWidget> createState() => _AdMobNativeAdWidgetState();
+}
+
+class _AdMobNativeAdWidgetState extends State<AdMobNativeAdWidget> {
+  admob.NativeAd? _admobNativeAd;
+  bool _isAdLoaded = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _initializeAd();
+  }
+
+  @override
+  void didUpdateWidget(covariant AdMobNativeAdWidget oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    // If the underlying ad object changes, dispose the old one and initialize the new one.
+    if (widget.nativeAd.adObject != oldWidget.nativeAd.adObject) {
+      _disposeOldAd();
+      _initializeAd();
+    }
+  }
+
+  void _initializeAd() {
+    // Ensure the adObject is of the expected AdMob NativeAd type.
+    if (widget.nativeAd.adObject is admob.NativeAd) {
+      _admobNativeAd = widget.nativeAd.adObject as admob.NativeAd;
+      _isAdLoaded = true;
+    } else {
+      _admobNativeAd = null;
+      _isAdLoaded = false;
+      // Log an error if the adObject is not the expected type.
+      debugPrint(
+        'AdMobNativeAdWidget: Expected admob.NativeAd, but received '
+        '${widget.nativeAd.adObject.runtimeType}. Ad will not be displayed.',
+      );
+    }
+  }
+
+  void _disposeOldAd() {
+    _admobNativeAd?.dispose();
+    _admobNativeAd = null;
+    _isAdLoaded = false;
+  }
+
+  @override
+  void dispose() {
+    _disposeOldAd();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (!_isAdLoaded || _admobNativeAd == null) {
+      // If the ad is not loaded or is of the wrong type, return an empty container.
+      return const SizedBox.shrink();
+    }
+
+    // Use the AdMob SDK's AdWidget to render the native ad.
+    return admob.AdWidget(ad: _admobNativeAd!);
+  }
+}