feat: IUniverse.OnTimeChanged event added

Engine.Core/Abstract/IUniverse.cs

@@ -32,6 +32,11 @@ public interface IUniverse : IEntity, IEnumerable<IUniverseObject>
     /// </summary>
     event UniverseObjectUnRegisteredEventHandler? OnUniverseObjectUnRegistered;
 
+    /// <summary>
+    /// Event triggered when <see cref="TimeScale"/> is changed on the <see cref="IUniverse"/>.
+    /// </summary>
+    event TimeScaleChangedEventHandler? OnTimeScaleChanged;
+
     /// <summary>
     /// Current time scale the <see cref="IUniverse"/> operates on.
     /// </summary>
@@ -83,6 +88,8 @@ public interface IUniverse : IEntity, IEnumerable<IUniverseObject>
     /// </summary>
     void PreDraw();
 
+    delegate void TimeScaleChangedEventHandler(IUniverse sender, float previousTimeScale);
+
     delegate void UpdateEventHandler(IUniverse sender, UniverseTime engineTime);
     delegate void PreDrawEventHandler(IUniverse sender);