feat: IActive interface added for hierarchy active state

Engine.Core/Abstract/IActive.cs

@@ -0,0 +1,19 @@
+namespace Syntriax.Engine.Core.Abstract;
+
+/// <summary>
+/// Represents an entity which can be active or not.
+/// </summary>
+public interface IActive
+{
+    /// <summary>
+    /// Event triggered when the <see cref="IsActive"/> state of the <see cref="IActive"/> changes.
+    /// </summary>
+    event ActiveChangedEventHandler? OnActiveChanged;
+
+    /// <summary>
+    /// The value indicating whether the <see cref="IActive"/> is enabled.
+    /// </summary>
+    bool IsActive { get; }
+
+    delegate void ActiveChangedEventHandler(IActive sender, bool previousState);
+}