fix(mobile): handle image stream completion when no image is emitted (#25984)

* Fix image cancellation to be stream-scoped instead of widget-scoped

* fix(OneFramePlaceholderImageStreamCompleter): make onLastListenerRemoved callback synchronous with removing the last listener

* fix(OneFrameMultiImageStreamCompleter): remove unnecessary blank line in code

* fix(OneFramePlaceholderImageStreamCompleter): cancel pending requests when only cache listener remains

* fix(OneFrameMultiImageStreamCompleter): ensure onLastListenerRemoved callback is invoked only once

mobile/lib/presentation/widgets/images/local_image_provider.dart

@@ -31,7 +31,7 @@ class LocalThumbProvider extends CancellableImageProvider<LocalThumbProvider>
         DiagnosticsProperty<String>('Id', key.id),
         DiagnosticsProperty<Size>('Size', key.size),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }
 
@@ -76,7 +76,7 @@ class LocalFullImageProvider extends CancellableImageProvider<LocalFullImageProv
         DiagnosticsProperty<String>('Id', key.id),
         DiagnosticsProperty<Size>('Size', key.size),
       ],
-      onDispose: cancel,
+      onLastListenerRemoved: cancel,
     );
   }