Closes https://github.com/ppy/osu/issues/34445.
The primary issue is that song select is the only one that supports
non-score sort mode, and therefore if any other component changes the
sort mode in a way opaque to song select to score, then song select will
lose the sort mode because it's using the global leaderboard manager's
state which will contain scores sorted by total.
Notably, the bug this is fixing requires specific circumstances. For
instance, it is not enough to just *start gameplay* for the bug to
manifest, because starting gameplay causes a working beatmap refetch:
https://github.com/ppy/osu/blob/4b73afd1957a9161e2956fc4191c8114d9958372/osu.Game/Screens/SelectV2/SongSelect.cs#L456-L457
which will trigger a *delayed schedule refetch* of the scores:
https://github.com/ppy/osu/blob/d2d3d14f1572ff8fc68fd01ea43c2ef68b5882fa/osu.Game/Screens/SelectV2/BeatmapLeaderboardWedge.cs#L235-L253
and because the refetch is thusly delayed, there's a very high chance it
*will not run before the screen is resumed* because the wedge will not
have its scheduler run until that point in time.
This conundrum is also because there is no test coverage for this,
because the above makes test coverage setup rather annoying.
This avoids needless web requests / server load, but also improves the
placeholder display. It used to update during ruleset changes three (or
more) times since it had no debounce and was reacting to multiple
changes. This is no longer the case.