Add function call option when getting output

Runtime/Scripts/Core/Neuron.cs

@@ -174,6 +174,8 @@ namespace NanoBrain {
 
 #if UNITY_MATHEMATICS
 
+        private readonly List<Action> fs = new();
+        
         /// <summary>
         /// The output value of the neuron
         /// </summary>
@@ -183,7 +185,11 @@ namespace NanoBrain {
         /// The output value of the neuron
         /// </summary>
         public virtual float3 outputValue {
-            get { return _outputValue; }
+            get { 
+                foreach (var f in fs)
+                    f();
+                return _outputValue;
+                 }
             set {
                 _outputValue = value;
                 if (this.isFiring)