It seems that no usages of `BeatmapSetInfo` detaches require files - a
`WorkingBeatmap` is always obtained before doing further lookups.
Therefore we can omit this include unless the detaching object is a
`BeatmapInfo`. A refetch is performed when retrieving a
`WorkingBeatmap` to complete the equation.
The async flow doesn't work great with the realm import process. We
might be able to improve on this going forward, but for the time being
adding a synchronous path seems safest.
After all, we are already an an asynchronous (dedicated) thread pool at
this point.