fix(ads): prevent native ad double dispose

Remove ad.dispose() call in onAdClosed to avoid premature disposal and potential crashes. The ad object is now disposed by AdmobNativeAdWidget when it is removed from the widget tree, preventing double dispose.

Author: fulleni

lib/ads/admob_ad_provider.dart

@@ -119,7 +119,9 @@ class AdMobAdProvider implements AdProvider {
         },
         onAdClosed: (ad) {
           _logger.info('Native Ad closed.');
-          ad.dispose();
+          // The ad object is now disposed by the AdmobNativeAdWidget (StatefulWidget)
+          // when it is removed from the widget tree. Removing this dispose call
+          // here prevents premature disposal and potential crashes.
         },
         onAdOpened: (ad) {
           _logger.info('Native Ad opened.');