CarouselVerticalAlignment
Controls the vertical placement of item content inside the Carousel, consistently across all variants (CarouselVariant.SlideShow, CarouselVariant.Theatre, CarouselVariant.Overflow).
Using a dedicated sealed class instead of androidx.compose.ui.Alignment.Vertical ensures the API is honest: only values that are actually honoured by all variants are exposed, preventing silent coercion of unsupported alignment values.