Use spans to improve performance in StreamExts.

Also avoid ReadBytes calls that allocate a buffer by either updating the stream position (if not interested in the bytes), by reusing an input buffer (if interested in the bytes), or using a stackalloc buffer to avoid the allocation (for small reads).

OpenRA.Game/Server/Connection.cs

@@ -64,7 +64,7 @@ namespace OpenRA.Server
 			ms.Write(0);
 			ms.Write(0);
 			ms.WriteByte((byte)OrderType.Ping);
-			ms.WriteArray(BitConverter.GetBytes(Game.RunTime));
+			ms.Write(Game.RunTime);
 			return ms.GetBuffer();
 		}