BookReader not loading higher-resolution images for high DPI screens by default

I've noticed on archive.org that the book reader doesn't take advantage of high resolution screens (e.g. on Macs and iPhones) and the images therefore look a bit blurry unless you zoom in. I see that this was fixed a few years ago in #378 by using srcset, but it looks like the code was rewritten since then; there's still support for it, controlled by useSrcSet in [src/BookReader/options.js](https://github.com/internetarchive/bookreader/blob/2d19d5537e3d5ecfe5532030cf6d679abd11709e/src/BookReader/options.js#L303) where the default is ```useSrcSet: false```, even though the comment above it says "On init, by default, we want to use srcSet for images." I tried changing that line to ```useSrcSet: true``` and it seems to work correctly that way. The default was changed from true to false in #651 and I don't see an explanation for why in the commit note. Was this intentional or could we change it back to true? I find it makes a big difference in legibility when reading books on small screens.