Update SpeedAdjustmentCollection.cs
# Conflicts: # osu.Game.Rulesets.Mania/UI/Column.cs
Covers the case where nested hit objects are involved.
Because not all playfields will be using this.
Also adds transition, uses IHasCurrentValue, combines Mod TestCases and more.
Previously we were looping over Update, when we should instead have been looping over UpdateSubTree.