Issue importing libheif as described in the docs.

According to the docs, libheif hast to be imported like this:
https://github.com/catdad-experiments/libheif-js?tab=readme-ov-file#usage

```

import libheif from 'https://cdn.jsdelivr.net/npm/libheif-js@1.19.8/libheif-wasm/libheif-bundle.mjs';

```

But this does not work (in the browser console, `libheif` is a function).
It only works if I add `window.libheif = libheif();` to the statement, why is that?

```

import libheif from 'https://cdn.jsdelivr.net/npm/libheif-js@1.19.8/libheif-wasm/libheif-bundle.mjs';
window.libheif = libheif();

```