Controlling item width (use-spring-carousel-item-wrapper)

To achieve more ambitious carousel initial layouts it's necessary to insert a dummy item and be able to size it.

This library forces all items to be the same width. Is there a way around that?

```
flex: `1 0 calc(100% / ${_itemsPerSlide} - ${
  (gutterRef.current * (_itemsPerSlide - 1)) / _itemsPerSlide
}px)`,
```