feat(picker.icons): implement unicode icon fetching and processing

[sassanh]

Description

Add unicode support for icons with data fetching from a URL.

Screenshots

[noirbizarre]

If you are interested, I made a script in my dotfiles to fetch and build a json file compatible with the existing custom_sources format.

It has the benefit of handling categories (you build your custom categories from official categories and character intervals).

It's doing the job for me but if you want to integrate this in Snacks directly, maybe add the official categories and filter out invisible chars, already included emojis (they already comes from Unicode too so they will be duplicated here) and pure text characters that you already have on the keyboard.

Note

The problem with ingesting all Unicode characters is that it generates a lot of entries, with lot of redundant names (so harder to match one) and some are not even visible characters. Unicode 17 is 297,334 chars and the file you use provide 40645 of them