[#973] ir: Listen and process Put/Delete events of Subnet contract

Define notification events, implement parsers. Add morph client of
Subnet contract. Listen, verify and approve events in Inner Ring app.

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

pkg/morph/client/subnet/get.go

@@ -0,0 +1,57 @@
+package morphsubnet
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/nspcc-dev/neofs-node/pkg/morph/client"
+)
+
+// GetPrm groups parameters of Get method of Subnet contract.
+type GetPrm struct {
+	cliPrm client.TestInvokePrm
+
+	args [1]interface{}
+}
+
+// SetID sets identifier of the subnet to be read in a binary NeoFS API protocol format.
+func (x *GetPrm) SetID(id []byte) {
+	x.args[0] = id
+}
+
+// GetRes groups resulting values of Get method of Subnet contract.
+type GetRes struct {
+	info []byte
+}
+
+// Info returns information about the subnet in a binary format of NeoFS API protocol.
+func (x GetRes) Info() []byte {
+	return x.info
+}
+
+var errEmptyResponse = errors.New("empty response")
+
+// Get reads the subnet through the call of the corresponding method of the Subnet contract.
+func (x *Client) Get(prm GetPrm) (*GetRes, error) {
+	prm.cliPrm.SetMethod("get")
+	prm.cliPrm.SetArgs(prm.args[:]...)
+
+	res, err := x.client.TestInvoke(prm.cliPrm)
+	if err != nil {
+		fmt.Println()
+		return nil, err
+	}
+
+	if len(res) == 0 {
+		return nil, errEmptyResponse
+	}
+
+	data, err := client.BytesFromStackItem(res[0])
+	if err != nil {
+		return nil, err
+	}
+
+	return &GetRes{
+		info: data,
+	}, nil
+}