fix: Add "Temp" and "Persistent" flags for RpcTarget options

com.unity.netcode.gameobjects/Runtime/Messaging/RpcTargets/BaseRpcTarget.cs

@@ -1,14 +1,35 @@
+using System;
+
 namespace Unity.Netcode
 {
-    public abstract class BaseRpcTarget
+    public abstract class BaseRpcTarget : IDisposable
     {
         protected NetworkManager m_NetworkManager;
+        private bool m_Locked;
+
+        internal void Lock()
+        {
+            m_Locked = true;
+        }
+
+        internal void Unlock()
+        {
+            m_Locked = false;
+        }
 
         internal BaseRpcTarget(NetworkManager manager)
         {
             m_NetworkManager = manager;
         }
 
+        protected void CheckLockBeforeDispose()
+        {
+            if (m_Locked)
+            {
+                throw new Exception($"RPC targets obtained through {nameof(RpcTargetUse)}.{RpcTargetUse.Temp} may not be disposed.");
+            }
+        }
+
         public abstract void Dispose();
 
         internal abstract void Send(NetworkBehaviour behaviour, ref RpcMessage message, NetworkDelivery delivery, RpcParams rpcParams);

com.unity.netcode.gameobjects/Runtime/Messaging/RpcTargets/DirectSendRpcTarget.cs

@@ -8,7 +8,7 @@ internal class DirectSendRpcTarget : BaseRpcTarget, IIndividualRpcTarget
 
         public override void Dispose()
         {
-
+            CheckLockBeforeDispose();
         }
 
         internal override void Send(NetworkBehaviour behaviour, ref RpcMessage message, NetworkDelivery delivery, RpcParams rpcParams)
@@ -25,5 +25,10 @@ internal DirectSendRpcTarget(NetworkManager manager) : base(manager)
         {
 
         }
+
+        internal DirectSendRpcTarget(ulong clientId, NetworkManager manager) : base(manager)
+        {
+            ClientId = clientId;
+        }
     }
 }

com.unity.netcode.gameobjects/Runtime/Messaging/RpcTargets/ProxyRpcTargetGroup.cs

@@ -56,6 +56,7 @@ internal ProxyRpcTargetGroup(NetworkManager manager) : base(manager)
 
         public override void Dispose()
         {
+            CheckLockBeforeDispose();
             if (!m_Disposed)
             {
                 TargetClientIds.Dispose();