[#236] api: Refactor caches: ObjectsList, Objects

Move ObjectsList from layer to cache package
Rename object_cache.go to objects.go

Signed-off-by: Angira Kekteeva <kira@nspcc.ru>

api/cache/objects_test.go

@@ -0,0 +1,41 @@
+package cache
+
+import (
+	"testing"
+	"time"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+	objecttest "github.com/nspcc-dev/neofs-api-go/pkg/object/test"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	cachesize = 10
+	lifetime  = time.Second * 5
+)
+
+func TestCache(t *testing.T) {
+	obj := objecttest.Object()
+	address := object.NewAddress()
+	address.SetContainerID(obj.ContainerID())
+	address.SetObjectID(obj.ID())
+
+	t.Run("check get", func(t *testing.T) {
+		cache := New(cachesize, lifetime)
+		err := cache.Put(*obj)
+		require.NoError(t, err)
+
+		actual := cache.Get(address)
+		require.Equal(t, obj, actual)
+	})
+
+	t.Run("check delete", func(t *testing.T) {
+		cache := New(cachesize, lifetime)
+		err := cache.Put(*obj)
+		require.NoError(t, err)
+
+		cache.Delete(address)
+		actual := cache.Get(address)
+		require.Nil(t, actual)
+	})
+}