chore: Added Initial Engine Code

Engine.Core/Exceptions/NotAssignedException.cs

@@ -0,0 +1,21 @@
+using System;
+using Syntriax.Engine.Core.Abstract;
+
+namespace Syntriax.Engine.Core.Exceptions;
+
+public class NotAssignedException : Exception
+{
+    public NotAssignedException() : base("The object has not been assigned.") { }
+    public NotAssignedException(string? message) : base(message) { }
+
+    public static NotAssignedException From<T1, T2>(T1 to, T2? value) where T1 : IAssignable
+        => new NotAssignedException($"{typeof(T2).Name} has not been assigned to {typeof(T1).Name}");
+
+    public static void Check<T1, T2>(T1 to, T2? value) where T1 : IAssignable
+    {
+        if (value is not null)
+            return;
+
+        throw From(to, value);
+    }
+}