Support React 19

[janie314]

Steps to reproduce the behavior:

1. Use ImageGallery with a React 19 repo.
2. You'll get an error like the following, and see that it can be fixed by downgrading to React 18.

src/App.tsx:36:8 - error TS2786: 'ImageGallery' cannot be used as a JSX component.
  Its type 'typeof ReactImageGallery' is not a valid JSX element type.
    Type 'typeof ReactImageGallery' is not assignable to type 'new (props: any) => Component<any, any, any>'.
      Construct signature return types 'ReactImageGallery' and 'Component<any, any, any>' are incompatible.
        The types returned by 'render()' are incompatible between these types.
          Type 'import("/home/janie/git/janie.page/photo-gallery/node_modules/@types/react-image-gallery/node_modules/@types/react/index").ReactNode' is not assignable to type 'React.ReactNode'.
            Type 'ReactElement<any, string | JSXElementConstructor<any>>' is not assignable to type 'ReactNode'.
              Property 'children' is missing in type 'ReactElement<any, string | JSXElementConstructor<any>>' but required in type 'ReactPortal'.

36       <ImageGallery items={images} slideInterval={10000} showNav={false} />

[janie314]

This is likely just #801 in a different form, based on how I'm using React 19.

This project may just be able to support React 19 as-is.