Move `IPlacementHandler` caching to interface

osu.Game/Rulesets/Edit/HitObjectComposer.cs

@@ -35,7 +35,6 @@ namespace osu.Game.Rulesets.Edit
     /// Responsible for providing snapping and generally gluing components together.
     /// </summary>
     /// <typeparam name="TObject">The base type of supported objects.</typeparam>
-    [Cached(Type = typeof(IPlacementHandler))]
     public abstract class HitObjectComposer<TObject> : HitObjectComposer, IPlacementHandler
         where TObject : HitObject
     {

osu.Game/Screens/Edit/Compose/IPlacementHandler.cs

@@ -1,10 +1,12 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using osu.Framework.Allocation;
 using osu.Game.Rulesets.Objects;
 
 namespace osu.Game.Screens.Edit.Compose
 {
+    [Cached]
     public interface IPlacementHandler
     {
         /// <summary>

osu.Game/Tests/Visual/PlacementBlueprintTestScene.cs

@@ -14,7 +14,6 @@
 
 namespace osu.Game.Tests.Visual
 {
-    [Cached(Type = typeof(IPlacementHandler))]
     public abstract class PlacementBlueprintTestScene : OsuManualInputManagerTestScene, IPlacementHandler
     {
         protected readonly Container HitObjectContainer;