Add stable marshal for owner id

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

refs/v2/marshal_test.go

@@ -0,0 +1,44 @@
+package v2
+
+import (
+	"crypto/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOwnerID_StableMarshal(t *testing.T) {
+	owner := make([]byte, 25)
+	_, err := rand.Read(owner)
+	require.NoError(t, err)
+
+	expectedOwner := new(OwnerID)
+	expectedOwner.Value = owner
+
+	gotOwner := new(OwnerID)
+
+	t.Run("small buffer", func(t *testing.T) {
+		_, err = expectedOwner.StableMarshal(make([]byte, 1))
+		require.Error(t, err)
+	})
+
+	t.Run("empty owner", func(t *testing.T) {
+		data, err := new(OwnerID).StableMarshal(nil)
+		require.NoError(t, err)
+
+		err = gotOwner.Unmarshal(data)
+		require.NoError(t, err)
+
+		require.Len(t, gotOwner.Value, 0)
+	})
+
+	t.Run("non empty owner", func(t *testing.T) {
+		data, err := expectedOwner.StableMarshal(nil)
+		require.NoError(t, err)
+
+		err = gotOwner.Unmarshal(data)
+		require.NoError(t, err)
+
+		require.Equal(t, expectedOwner, gotOwner)
+	})
+}