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

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

mtglib/internal/relay/relay.go

 	"io"
 
 	"github.com/9seconds/mtg/v2/essentials"
+	"github.com/9seconds/mtg/v2/mtglib/internal/tls"
 )
 
 func Relay(ctx context.Context, log Logger, telegramConn, clientConn essentials.Conn) {
 }
 
 func pump(log Logger, src, dst essentials.Conn, direction string) {
-	var buf [copyBufferSize]byte
+	var buf [tls.MaxRecordPayloadSize]byte
 
 	defer src.CloseRead()  //nolint: errcheck
 	defer dst.CloseWrite() //nolint: errcheck