Integrate keymap-drawer into flake

[MattSturgeon]

Refactor keymap-drawer so that is is part of the flake.

• Build keymap-drawer using poetry2nix
• Re-implement CI logic/scripts as nix builds
• Port CI to flake builds
• Remove old scripts
• Remove symlink hack-fix, needs parse: keyboard name detection fails for files in nix store caksoylar/keymap-drawer#84
• Fix SVG icons (can't download in a pure env)
  • glyph_urls might support file: URLs? If not open upstream request.
  • use_local_cache may need to be disabled, depending on where it writes to