[#218] Support SplitInfo structure

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

pkg/object/splitinfo_test.go

@@ -0,0 +1,42 @@
+package object_test
+
+import (
+	"crypto/rand"
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSplitInfo(t *testing.T) {
+	s := object.NewSplitInfo()
+	splitID := object.NewSplitID()
+	lastPart := generateID()
+	link := generateID()
+
+	s.SetSplitID(splitID)
+	require.Equal(t, splitID, s.SplitID())
+
+	s.SetLastPart(lastPart)
+	require.Equal(t, lastPart, s.LastPart())
+
+	s.SetLink(link)
+	require.Equal(t, link, s.Link())
+
+	t.Run("to and from v2", func(t *testing.T) {
+		v2 := s.ToV2()
+		newS := object.NewSplitInfoFromV2(v2)
+
+		require.Equal(t, s, newS)
+	})
+}
+
+func generateID() *object.ID {
+	var buf [32]byte
+	_, _ = rand.Read(buf[:])
+
+	id := object.NewID()
+	id.SetSHA256(buf)
+
+	return id
+}