That was a bad one... `ModelBackedDrawable` has a default of 0ms load delay, while previously the wrapper created for beatmap set cover used default 500ms, this change is bringing the load delay back, to avoid firing hundreds of web requests just when doing a quick long scroll on beatmap listing.
Applies two changes:
- Use `TransformImmediately` which achieves the same wanted transition behaviour without any issues.
- Move the transition behaviour override into `BeatmapListingSearchControl` in a nested subclass of `UpdateableBeatmapSetCover`.
