Make column + stage cached

osu.Game.Rulesets.Mania/UI/Column.cs

@@ -19,6 +19,7 @@ using osuTK;
 
 namespace osu.Game.Rulesets.Mania.UI
 {
+    [Cached]
     public class Column : ScrollingPlayfield, IKeyBindingHandler<ManiaAction>, IHasAccentColour
     {
         public const float COLUMN_WIDTH = 80;

osu.Game.Rulesets.Mania/UI/ManiaStage.cs

@@ -23,6 +23,7 @@ namespace osu.Game.Rulesets.Mania.UI
     /// <summary>
     /// A collection of <see cref="Column"/>s.
     /// </summary>
+    [Cached]
     public class ManiaStage : ScrollingPlayfield
     {
         public const float COLUMN_SPACING = 1;