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Now only used in character position syncing, but some other entities may also have an use for it (e.g. discarding outdated data)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

@@ -625,6 +625,8 @@ namespace Barotrauma.Networking
         {
             NetOutgoingMessage outmsg = server.CreateMessage();
             outmsg.Write((byte)ServerPacketHeader.UPDATE_INGAME);
+            
+            outmsg.Write((float)NetTime.Now);
 
             outmsg.Write((byte)ServerNetObject.SYNC_IDS);
             outmsg.Write(c.lastSentChatMsgID); //send this to client so they know which chat messages weren't received by the server