Returned by useFading to useUpvotedList and usePlaylist. The
list keeps showing an item while it is in fading.
startFading: (id: string) => void
Does nothing when id is already fading.
cancelFading: (id: string) => void
Called when the removal is undone, so that the item stays.
cancelAll: () => void
Called when the list is replaced, as by another user's upvotes.