~aleteoryx/lfm_embed

ref: adc1a486faf473eb7d993ca5df78485f0938d1d0 lfm_embed/src/cache d---------
Fixed backend API, again.

Turns out track.getInfo just doesn't feel like serving image data anymore, even though the example response shows it. I love last.fm so much.
Lua dev mode functional
whitelist -> allowlist
Add SPDX info to all files
Move caching to src/cache/; Finalize API parsing fixes

Font and user cache code has been moved to special files, independant from src/config.rs

API parsing changes have been properly tested, and last.fm API JSON is now trace-logged for debugging convenience.