[#506] container: Use uint64 for epoch type

It is `uint64` in netmap source interfaces and other code.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/core/container/storage.go

@@ -28,7 +28,7 @@ type DelInfo struct {
 	Owner user.ID
 
 	// Epoch indicates when the container was removed.
-	Epoch int
+	Epoch uint64
 }
 
 // Source is an interface that wraps

pkg/morph/client/container/deletion_info.go

@@ -63,13 +63,13 @@ func (c *Client) DeletionInfo(cid []byte) (*containercore.DelInfo, error) {
 		return nil, fmt.Errorf("could not decode container owner id (%s): %w", deletionInfoMethod, err)
 	}
 
-	epoch, err := client.IntFromStackItem(arr[1])
+	epoch, err := client.BigIntFromStackItem(arr[1])
 	if err != nil {
 		return nil, fmt.Errorf("could not get byte array of container signature (%s): %w", deletionInfoMethod, err)
 	}
 
 	return &containercore.DelInfo{
 		Owner: owner,
-		Epoch: int(epoch),
+		Epoch: epoch.Uint64(),
 	}, nil
 }