Fix stack leniency not applying immediately after change

[bdach]

RFC. Closes #20675.

I don't love this diff and I'm a bit scared of this change, but the last time this was attempted to be fixed the end result was #25467, so in comparison this looks like it may have a chance of maybe passing review.

Will add some self-review comments in a sec because this is a bit counterintuitive and I wasn't sure how much of this was deserving comments (provided this diff survives the initial eye test even). Can also try and add tests for this if this is deemed a viable route forward.

[bdach]

This is the primary fix and it works by addressing the thing mentioned in #20675 (comment), namely reading from the correct BeatmapInfo instance.

I audited both beatmap processors of ours that actually do stuff (osu! and catch), and all of the properties they touch aside from BeatmapInfo are proxied in EditorBeatmap forward to PlayableBeatmap, so from that angle this seems safe-ish.

[bdach]

This bypasses the following guard:

osu/osu.Game/Screens/Edit/EditorBeatmap.cs

Lines 349 to 350 in a8a2e54

	if (batchPendingUpdates.Count == 0 && batchPendingDeletes.Count == 0 && batchPendingInserts.Count == 0)
	return;

Compare:

osu/osu.Game/Screens/Edit/Setup/DifficultySection.cs

Lines 119 to 132 in a8a2e54

	private void updateValues()
	{
	// for now, update these on commit rather than making BeatmapMetadata bindables.
	// after switching database engines we can reconsider if switching to bindables is a good direction.
	Beatmap.Difficulty.CircleSize = CircleSizeSlider.Current.Value;
	Beatmap.Difficulty.DrainRate = HealthDrainSlider.Current.Value;
	Beatmap.Difficulty.ApproachRate = ApproachRateSlider.Current.Value;
	Beatmap.Difficulty.OverallDifficulty = OverallDifficultySlider.Current.Value;
	Beatmap.Difficulty.SliderMultiplier = BaseVelocitySlider.Current.Value;
	Beatmap.Difficulty.SliderTickRate = TickRateSlider.Current.Value;
	Beatmap.UpdateAllHitObjects();
	Beatmap.SaveState();
	}

[bdach]

This hard cast needs to be gone for the EditorBeatmap change to have a chance of working, because EditorBeatmap is not a Beatmap<OsuHitObject>. The catch processor strangely does not do this sort of casting and does nice proper soft casts instead.

As an "optimisation" (reducing iterator and list allocations) I added the soft-cast of Beatmap.HitObjects to List<OsuHitObject>.

[smoogipoo]

I think this is fine