Support JPEG XL (`.jxl`)

[42willow]

Gnome also delivers their wallpapers as SVG or WebP.

Gnome now delivers their wallpapers in SVG and JXL formats; it would be nice if swww supported both... :)

Originally posted by @loserMcloser in #48

---

also see wbg's implementation here: https://codeberg.org/dnkl/wbg

[42willow]

oops sorry, blocked by https://github.com/image-rs/image/issues/1765

[AcroBanwagon]

image-rs/image#1765 should no longer be an issue. The image crate should now support jxl via the jxl-oxide crate. Please see https://github.com/image-rs/image/pull/2372 and https://github.com/tirr-c/jxl-oxide/pull/480.