What

This PR fixes #167.

Why

Setting GalleryButtonType.none hides all action buttons (torch and camera switch included).
It was requested to implement a way to disable only the gallery button while keeping other controls visible.

How

Introduced a new ScannerAction enum and enabledActionButtons parameter, allowing users to specify exactly which icons should be displayed.
For example:

AiBarcodeScanner(
    galleryButtonType: GalleryButtonType.icon,
    enabledActionButtons: const {
      ScannerAction.cameraSwitch,
      ScannerAction.torch,
    },
    onDetect: (BarcodeCapture capture) {
      /// Do something with the barcode
    },
  )