feat(ads): implement AdMobAdProvider for Google AdMob integration

- Add AdMobAdProvider class implementing AdProvider interface
- Include initialization of Google Mobile Ads SDK
- Implement native ad loading for AdMob with platform-specific unit IDs
- Add logging for ad events and errors
- Support Android, iOS, and Web platforms

Author: fulleni

lib/ads/admob_ad_provider.dart

@@ -0,0 +1,119 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/ad_provider.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart';
+import 'package:logging/logging.dart';
+
+/// {@template admob_ad_provider}
+/// A concrete implementation of [AdProvider] for Google AdMob.
+///
+/// This class handles the initialization of the Google Mobile Ads SDK
+/// and the loading of native ads specifically for AdMob.
+/// {@endtemplate}
+class AdMobAdProvider implements AdProvider {
+  /// {@macro admob_ad_provider}
+  AdMobAdProvider({Logger? logger}) : _logger = logger ?? Logger('AdMobAdProvider');
+
+  final Logger _logger;
+
+  /// The AdMob Native Ad Unit ID for Android.
+  ///
+  /// This should be replaced with your production Ad Unit ID.
+  /// For testing, use `ca-app-pub-3940256099942544/2247696110`.
+  static const String _androidNativeAdUnitId =
+      'ca-app-pub-3940256099942544/2247696110';
+
+  /// The AdMob Native Ad Unit ID for iOS.
+  ///
+  /// This should be replaced with your production Ad Unit ID.
+  /// For testing, use `ca-app-pub-3940256099942544/3986624511`.
+  static const String _iosNativeAdUnitId =
+      'ca-app-pub-3940256099942544/3986624511';
+
+  /// The AdMob Native Ad Unit ID for Web.
+  ///
+  /// AdMob does not officially support native ads on web. This is a placeholder.
+  /// For testing, use `ca-app-pub-3940256099942544/2247696110` (Android test ID).
+  static const String _webNativeAdUnitId =
+      'ca-app-pub-3940256099942544/2247696110';
+
+  /// Returns the appropriate native ad unit ID based on the platform.
+  String get _nativeAdUnitId {
+    if (kIsWeb) {
+      return _webNativeAdUnitId;
+    } else if (defaultTargetPlatform == TargetPlatform.android) {
+      return _androidNativeAdUnitId;
+    } else if (defaultTargetPlatform == TargetPlatform.iOS) {
+      return _iosNativeAdUnitId;
+    }
+    return ''; // Fallback for unsupported platforms
+  }
+
+  @override
+  Future<void> initialize() async {
+    _logger.info('Initializing Google Mobile Ads SDK...');
+    try {
+      await MobileAds.instance.initialize();
+      _logger.info('Google Mobile Ads SDK initialized successfully.');
+    } catch (e) {
+      _logger.severe('Failed to initialize Google Mobile Ads SDK: $e');
+      // TODO(fulleni): Depending on requirements, you might want to rethrow or handle this more gracefully.
+      // For now, we log and continue, as ad loading might still work in some cases.
+    }
+  }
+
+  @override
+  Future<NativeAd?> loadNativeAd() async {
+    if (_nativeAdUnitId.isEmpty) {
+      _logger.warning('No native ad unit ID configured for this platform.');
+      return null;
+    }
+
+    _logger.info('Attempting to load native ad from unit ID: $_nativeAdUnitId');
+
+    final completer = Completer<NativeAd?>();
+
+    final ad = NativeAd(
+      adUnitId: _nativeAdUnitId,
+      factoryId: 'listTile', // This ID must match a factory in your native code
+      request: const AdRequest(),
+      listener: NativeAdListener(
+        onAdLoaded: (ad) {
+          _logger.info('Native Ad loaded successfully.');
+          completer.complete(ad as NativeAd);
+        },
+        onAdFailedToLoad: (ad, error) {
+          _logger.severe('Native Ad failed to load: $error');
+          ad.dispose();
+          completer.complete(null);
+        },
+        onAdClicked: (ad) {
+          _logger.info('Native Ad clicked.');
+        },
+        onAdImpression: (ad) {
+          _logger.info('Native Ad impression recorded.');
+        },
+        onAdClosed: (ad) {
+          _logger.info('Native Ad closed.');
+          ad.dispose();
+        },
+        onAdOpened: (ad) {
+          _logger.info('Native Ad opened.');
+        },
+        onAdWillDismissScreen: (ad) {
+          _logger.info('Native Ad will dismiss screen.');
+        },
+      ),
+    );
+
+    try {
+      await ad.load();
+    } catch (e) {
+      _logger.severe('Error during native ad load: $e');
+      completer.complete(null);
+    }
+
+    return completer.future;
+  }
+}