Decrease relay buffer size

Even if it makes sense to have a huge buffers, we do artificial delays
now. In that case we could achieve the same results with a lower buffer.
If not, then we won't send a packet bigger that this value

mtglib/internal/relay/init.go

@@ -1,9 +1,5 @@
 package relay
 
-const (
-	copyBufferSize = 64 * 1024
-)
-
 type Logger interface {
 	Printf(msg string, args ...any)
 }