[#39] accounting: Move decimal structure to SDK

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

accounting/decimal_test.go

@@ -0,0 +1,44 @@
+package accounting_test
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-sdk-go/accounting"
+	test "github.com/nspcc-dev/neofs-sdk-go/accounting/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecimal(t *testing.T) {
+	const v, p = 4, 2
+
+	d := accounting.NewDecimal()
+	d.SetValue(v)
+	d.SetPrecision(p)
+
+	require.EqualValues(t, v, d.Value())
+	require.EqualValues(t, p, d.Precision())
+}
+
+func TestDecimalEncoding(t *testing.T) {
+	d := test.GenerateDecimal()
+
+	t.Run("binary", func(t *testing.T) {
+		data, err := d.Marshal()
+		require.NoError(t, err)
+
+		d2 := accounting.NewDecimal()
+		require.NoError(t, d2.Unmarshal(data))
+
+		require.Equal(t, d, d2)
+	})
+
+	t.Run("json", func(t *testing.T) {
+		data, err := d.MarshalJSON()
+		require.NoError(t, err)
+
+		d2 := accounting.NewDecimal()
+		require.NoError(t, d2.UnmarshalJSON(data))
+
+		require.Equal(t, d, d2)
+	})
+}