[#425] Adapt the Client's refactoring to the interface

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

pkg/network/cache/client.go

@@ -11,7 +11,7 @@ type (
 	// already created clients.
 	ClientCache struct {
 		mu      *sync.RWMutex
-		clients map[string]*client.Client
+		clients map[string]client.Client
 		opts    []client.Option
 	}
 )
@@ -21,13 +21,13 @@ type (
 func NewSDKClientCache(opts ...client.Option) *ClientCache {
 	return &ClientCache{
 		mu:      new(sync.RWMutex),
-		clients: make(map[string]*client.Client),
+		clients: make(map[string]client.Client),
 		opts:    opts,
 	}
 }
 
 // Get function returns existing client or creates a new one.
-func (c *ClientCache) Get(address string) (*client.Client, error) {
+func (c *ClientCache) Get(address string) (client.Client, error) {
 	c.mu.RLock()
 	if cli, ok := c.clients[address]; ok {
 		// todo: check underlying connection neofs-api-go#196