[#265] innerring: Add client cache

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

pkg/innerring/rpc.go

@@ -0,0 +1,24 @@
+package innerring
+
+import (
+	"crypto/ecdsa"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/client"
+	"github.com/nspcc-dev/neofs-node/pkg/network/cache"
+)
+
+type ClientCache struct {
+	cache *cache.ClientCache
+	key   *ecdsa.PrivateKey
+}
+
+func newClientCache(key *ecdsa.PrivateKey) *ClientCache {
+	return &ClientCache{
+		cache: cache.NewSDKClientCache(),
+		key:   key,
+	}
+}
+
+func (c *ClientCache) Get(address string, opts ...client.Option) (*client.Client, error) {
+	return c.cache.Get(c.key, address, opts...)
+}