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

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

[42willow]

oops sorry, blocked by image-rs/image#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 image-rs/image#2372 and tirr-c/jxl-oxide#480.