refactor: add frame info duration loop that checks the number of image info to add

[fernan542]

I noticed that if the current frame contains the same image info, they are only considered as one frame which makes the actual gif unable to play the complete gif frame/duration.

To make things clear, here's an example gif:

The first( image with #1) frame's duration is 4 seconds but when played, it only shows 1 frame since they're all the same. Then the rest is fine since they're all playing at 1 sec, meaning 1 frame.

So to fix that, I added a validator that loop and checks whether the actual duration/frame was added to the list of ImageInfos.

    for (int sec = 1; sec <= duration; sec++) {
      infos.add(ImageInfo(image: frameInfo.image));
    }

Another thing, I replaced this deprecated method:

ui.Codec codec = await PaintingBinding.instance.instantiateImageCodec(bytes);

'instantiateImageCodec' is deprecated and shouldn't be used. Use instantiateImageCodecFromBuffer with an ImmutableBuffer instance instead. This feature was deprecated after v2.13.0-1.0.pre..

by using the suggested:

  final buffer = await ImmutableBuffer.fromUint8List(bytes);
  ui.Codec codec =
      await PaintingBinding.instance.instantiateImageCodecFromBuffer(buffer);

[diegogarciar]

this doesn't work if the duration of a frame is <0 as the loop conditions never met

[sipanpetrosyan]

final buffer = await ImmutableBuffer.fromUint8List(bytes); ui.Codec codec = await PaintingBinding.instance.instantiateImageCodecFromBuffer(buffer);

  I approve these changes. This will help to avoid the `instantiateImageCodec()` deprecation issue.