Add extension method to detect and isolate realm collection-level changes

osu.Game/Database/RealmExtensions.cs

@@ -4,6 +4,8 @@
 using System;
 using Realms;
 
+#nullable enable
+
 namespace osu.Game.Database
 {
     public static class RealmExtensions
@@ -22,5 +24,14 @@ namespace osu.Game.Database
             transaction.Commit();
             return result;
         }
+
+        /// <summary>
+        /// Whether the provided change set has changes to the top level collection.
+        /// </summary>
+        /// <remarks>
+        /// Realm subscriptions fire on both collection and property changes (including *all* nested properties).
+        /// Quite often we only care about changes at a collection level. This can be used to guard and early-return when no such changes are in a callback.
+        /// </remarks>
+        public static bool HasCollectionChanges(this ChangeSet changes) => changes.InsertedIndices.Length > 0 || changes.DeletedIndices.Length > 0 || changes.Moves.Length > 0;
     }
 }