Due to the use of bindable flow provided by `BeatmapDifficultyCache` in
this usage, the display would briefly flash to zero while difficulty
calculation was still running (as there is no way for a consumer of the
provided bindable to know whether the returned 0 is an actual 0 SR or a
"pending" calculation).
While I hope to fix this by making the bindable flow return nullable
values, I think this particular use case works better with non-bindable
flow so have switched across to that.
9f3ceb99eb