InGame update messages include a timestamp which is passed to the ClientRead methods

Now only used in character position syncing, but some other entities may also have an use for it (e.g. discarding outdated data)

Subsurface/Source/Networking/INetSerializable.cs

@@ -22,6 +22,6 @@ namespace Barotrauma.Networking
         UInt32 NetStateID { get; }
 
         void ServerWrite(NetOutgoingMessage msg, Client c);
-        void ClientRead(NetIncomingMessage msg);
+        void ClientRead(NetIncomingMessage msg, float sendingTime);
     }
 }