fix: add custom event handler if not default

Pilz.Plugins.Advanced/PluginFeatureController.cs

@@ -28,7 +28,7 @@ namespace Pilz.Plugins.Advanced
         /// </summary>
         public static PluginFeatureController Instance { get; private set; } = new();
 
-        private readonly List<PluginFeature> features = new();
+        private readonly HashSet<PluginFeature> features = new();
 
         /// <summary>
         /// A wrapper of all registred <see cref="PluginFeature"/> instances.
@@ -78,7 +78,7 @@ namespace Pilz.Plugins.Advanced
 
             public virtual IEnumerable<PluginFeature> GetAll()
             {
-                return controller.features.AsReadOnly();
+                return controller.features.ToArray();
             }
 
             public virtual IEnumerable<PluginFeature> Get(string featureType)