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/Server.cs

@@ -707,7 +707,7 @@ namespace OpenRA.Server
 			ms.Write(data.Length + 4);
 			ms.Write(client);
 			ms.Write(frame);
-			ms.WriteArray(data);
+			ms.Write(data);
 			return ms.GetBuffer();
 		}