lneto rework: Require explicit BackoffStrategy in all APIs (#116)

* make backoff explicit API

* fix tests to use explicit backoff

* fix examples with explicit tcp

udp/conn_test.go

@@ -4,7 +4,9 @@ import (
 	"encoding/binary"
 	"net/netip"
 	"testing"
+	"time"
 
+	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/internal"
 )
 
@@ -26,6 +28,7 @@ func newTestConn(t *testing.T) *Conn {
 		TxBuf:       make([]byte, 256),
 		RxQueueSize: 4,
 		TxQueueSize: 4,
+		RWBackoff:   backoffYield,
 	})
 	if err != nil {
 		t.Fatal(err)
@@ -239,3 +242,7 @@ func TestConn_FrameOffset(t *testing.T) {
 		t.Fatalf("got %q, want %q", string(buf[:n]), "hi")
 	}
 }
+
+func backoffYield(backoffs uint) time.Duration {
+	return lneto.BackoffFlagGosched
+}