[#189] sdk/netmap: Refactor Replica type

Replace alias to v2 type Replica with v2-compatible implementation.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/netmap/replica_test.go

@@ -0,0 +1,36 @@
+package netmap
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/netmap"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReplicaFromV2(t *testing.T) {
+	rV2 := new(netmap.Replica)
+	rV2.SetCount(3)
+	rV2.SetSelector("selector")
+
+	r := NewReplicaFromV2(rV2)
+
+	require.Equal(t, rV2, r.ToV2())
+}
+
+func TestReplica_Count(t *testing.T) {
+	r := NewReplica()
+	c := uint32(3)
+
+	r.SetCount(c)
+
+	require.Equal(t, c, r.Count())
+}
+
+func TestReplica_Selector(t *testing.T) {
+	r := NewReplica()
+	s := "some selector"
+
+	r.SetSelector(s)
+
+	require.Equal(t, s, r.Selector())
+}