refactor(ads): improve ad navigator observer and interstitial ad handling

- Refactor AdNavigatorObserver to use AdThemeStyle and handle only PageRoutes
- Add InterstitialAd model for better ad management
- Remove unnecessary dependencies and simplify ad loading process
- Update logging and ad display logic

Author: fulleni

lib/ads/ad_navigator_observer.dart

@@ -2,11 +2,12 @@ import 'dart:async';
 
 import 'package:core/core.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/ad_service.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/ad_theme_style.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/models/interstitial_ad.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/app/bloc/app_bloc.dart';
 import 'package:logging/logging.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart' as admob;
 
 /// {@template ad_navigator_observer}
 /// A [NavigatorObserver] that listens to route changes and triggers
@@ -25,39 +26,36 @@ class AdNavigatorObserver extends NavigatorObserver {
   AdNavigatorObserver({
     required this.appBloc,
     required this.adService,
+    required AdThemeStyle adThemeStyle,
     Logger? logger,
-  }) : _logger = logger ?? Logger('AdNavigatorObserver');
+  })  : _logger = logger ?? Logger('AdNavigatorObserver'),
+        _adThemeStyle = adThemeStyle;
 
   final AppBloc appBloc;
   final AdService adService;
   final Logger _logger;
-
-  /// Tracks the number of page transitions since the last interstitial ad was shown.
-  /// This is managed by the AppBloc.
+  final AdThemeStyle _adThemeStyle;
 
   @override
   void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
     super.didPush(route, previousRoute);
     _logger.info('Route pushed: ${route.settings.name}');
-    _handlePageTransition();
+    _handlePageTransition(route);
   }
 
   @override
   void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
     super.didPop(route, previousRoute);
     _logger.info('Route popped: ${route.settings.name}');
-    _handlePageTransition();
+    _handlePageTransition(route);
   }
 
   /// Handles a page transition event.
   ///
   /// Dispatches an [AppPageTransitioned] event to the [AppBloc] to update
   /// the transition count and potentially trigger an interstitial ad.
-  void _handlePageTransition() {
-    // Only consider actual page routes, not overlays or dialogs.
-    // This check is a simplification; a more robust solution might inspect
-    // route types or use GoRouter's specific navigation events.
-    if (navigator?.currentRoutes.last.settings.name != null) {
+  void _handlePageTransition(Route<dynamic> route) {
+    if (route is PageRoute && route.settings.name != null) {
       appBloc.add(const AppPageTransitioned());
     }
   }
@@ -67,7 +65,6 @@ class AdNavigatorObserver extends NavigatorObserver {
   /// This method is called by the [AppBloc] when it determines an ad is due.
   Future<void> showInterstitialAd() async {
     final remoteConfig = appBloc.state.remoteConfig;
-    final user = appBloc.state.user;
 
     if (remoteConfig == null || !remoteConfig.adConfig.enabled) {
       _logger.info('Interstitial ads disabled or remote config not available.');
@@ -82,20 +79,10 @@ class AdNavigatorObserver extends NavigatorObserver {
       return;
     }
 
-    // Create AdThemeStyle from current theme for ad loading.
-    // This requires a BuildContext, which is not directly available here.
-    // The AppBloc will need to provide the AdThemeStyle or the AdService
-    // will need to be able to create it. For now, we'll assume a default
-    // or that the AdService can handle it.
-    //
-    // TODO(fulleni): Revisit how AdThemeStyle is passed for interstitial ads.
-    // For now, a placeholder AdThemeStyle is used.
-    final adThemeStyle = AdThemeStyle.fromTheme(ThemeData());
-
     _logger.info('Attempting to load interstitial ad...');
     final interstitialAd = await adService.getInterstitialAd(
       adConfig: adConfig,
-      adThemeStyle: adThemeStyle,
+      adThemeStyle: _adThemeStyle,
     );
 
     if (interstitialAd != null) {