[example][RgbaImage] Avoid use DecorderCallback which is removed after Flutter SDK 3.16

[littleGnAl]

The DecorderCallback was deprecated after v2.13.0-1.0.pre, and removed after 3.16.x

@Deprecated(
  'Use ImageDecoderCallback with ImageProvider.loadImage instead. '
  'This feature was deprecated after v2.13.0-1.0.pre.',
)
typedef DecoderCallback = Future<ui.Codec> Function(Uint8List buffer, {int? cacheWidth, int? cacheHeight, bool allowUpscaling});

But we need to compatible with the Flutter SDK 2.10.x, so we need to avoid directly using the ImageProvider