refactor(ads): remove obsolete ad disposal comments from AdMobAdProvider

Removed comments related to ad disposal from the `onAdFailedToLoad` and `onTimeout` callbacks in `AdMobAdProvider`.

Since the ad lifecycle is now exclusively managed by the `InlineAdCacheService`, this disposal logic (and the comments referring to it) is no longer relevant in the provider. This change clarifies the provider's role, which is solely to load ads, not to manage their disposal on failure.

Author: fulleni

lib/ads/admob_ad_provider.dart

@@ -88,7 +88,10 @@ class AdMobAdProvider implements AdProvider {
         },
         onAdFailedToLoad: (ad, error) {
           _logger.severe('AdMobAdProvider: Native Ad failed to load: $error');
-          // Ad disposal is now handled by InlineAdCacheService
+          // On a failed load, we do not dispose the ad object. The ad object
+          // is managed by the google_mobile_ads plugin and will be garbage
+          // collected. Completing with null signals the failure to the
+          // caller.
           completer.complete(null);
         },
         onAdClicked: (ad) {
@@ -120,7 +123,6 @@ class AdMobAdProvider implements AdProvider {
       const Duration(seconds: _adLoadTimeout),
       onTimeout: () {
         _logger.warning('AdMobAdProvider: Native ad loading timed out.');
-        // Ad disposal is now handled by InlineAdCacheService
         completer.complete(null);
         return null;
       },
@@ -179,7 +181,10 @@ class AdMobAdProvider implements AdProvider {
         },
         onAdFailedToLoad: (ad, error) {
           _logger.severe('AdMobAdProvider: Banner Ad failed to load: $error');
-          // Ad disposal is now handled by InlineAdCacheService
+          // On a failed load, we do not dispose the ad object. The ad object
+          // is managed by the google_mobile_ads plugin and will be garbage
+          // collected. Completing with null signals the failure to the
+          // caller.
           completer.complete(null);
         },
         onAdOpened: (ad) {
@@ -205,7 +210,6 @@ class AdMobAdProvider implements AdProvider {
       const Duration(seconds: _adLoadTimeout),
       onTimeout: () {
         _logger.warning('AdMobAdProvider: Banner ad loading timed out.');
-        // Ad disposal is now handled by InlineAdCacheService
         completer.complete(null);
         return null;
       },