[#556] morph/neofs: Implement contract client

Implement NeoFS contact's client which is responsible for collecting call
arguments and parsing stack items. Initially key binding and unbinding are
supported.

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

pkg/morph/client/neofs/bind.go

@@ -0,0 +1,63 @@
+package neofscontract
+
+import (
+	"fmt"
+)
+
+// BindKeysArgs groups the arguments
+// of key binding call.
+type BindKeysArgs struct {
+	commonBindArgs
+}
+
+// UnbindKeysArgs groups the arguments
+// of key unbinding call.
+type UnbindKeysArgs struct {
+	commonBindArgs
+}
+
+type commonBindArgs struct {
+	scriptHash []byte // script hash of account identifier
+
+	keys [][]byte // list of serialized public keys
+}
+
+// SetScriptHash sets script hash of the NeoFS account identifier.
+func (x *commonBindArgs) SetScriptHash(v []byte) {
+	x.scriptHash = v
+}
+
+// SetKeys sets list of public keys in a binary format.
+func (x *commonBindArgs) SetKeys(v [][]byte) {
+	x.keys = v
+}
+
+// BindKeys invokes the call of key binding method
+// of NeoFS contract.
+func (x *Client) BindKeys(args BindKeysArgs) error {
+	err := x.client.Invoke(
+		x.bindKeysMethod,
+		args.scriptHash,
+		args.keys,
+	)
+	if err != nil {
+		return fmt.Errorf("could not invoke method (%s): %w", x.bindKeysMethod, err)
+	}
+
+	return nil
+}
+
+// UnbindKeys invokes the call of key unbinding method
+// of NeoFS contract.
+func (x *Client) UnbindKeys(args UnbindKeysArgs) error {
+	err := x.client.Invoke(
+		x.unbindKeysMethod,
+		args.scriptHash,
+		args.keys,
+	)
+	if err != nil {
+		return fmt.Errorf("could not invoke method (%s): %w", x.unbindKeysMethod, err)
+	}
+
+	return nil
+}