fix: Prevent multiple NetworkTransforms on the same object (#1258)

Author: TwoTenPvP

com.unity.netcode.gameobjects/Components/NetworkTransform.cs

@@ -10,6 +10,7 @@ namespace Unity.Netcode.Components
     /// NetworkTransform will read the underlying transform and replicate it to clients.
     /// The replicated value will be automatically be interpolated (if active) and applied to the underlying GameObject's transform
     /// </summary>
+    [DisallowMultipleComponent]
     [AddComponentMenu("Netcode/" + nameof(NetworkTransform))]
     [DefaultExecutionOrder(100000)] // this is needed to catch the update time after the transform was updated by user scripts
     public class NetworkTransform : NetworkBehaviour

com.unity.netcode.gameobjects/Samples/ClientNetworkTransform/Scripts/ClientNetworkTransform.cs

@@ -1,11 +1,13 @@
 using Unity.Netcode.Components;
+using UnityEngine;
 
 namespace Unity.Netcode.Samples
 {
     /// <summary>
     /// Used for syncing a transform with client side changes. This includes host. Pure server as owner isn't supported by this. Please use NetworkTransform
     /// for transforms that'll always be owned by the server.
     /// </summary>
+    [DisallowMultipleComponent]
     public class ClientNetworkTransform : NetworkTransform
     {
         /// <summary>