feat!: GetRequiredBehaviour/HierarchyObject methods added for cleaner null handling

Engine.Core/Exceptions/BehaviourNotFoundException.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace Syntriax.Engine.Core.Exceptions;
+
+public class BehaviourNotFoundException(string? message) : Exception(message)
+{
+    public static NotAssignedException FromType<TBehaviour>()
+        => new($"{typeof(TBehaviour).FullName} was not found");
+}