anki: add module

[JuneStepp]

Description

Anki is a popular spaced repetition flashcards learning program. This PR introduces a module for configuring Anki settings and add-ons. It is the counterpart to my nixpkgs PR that has now reached unstable. ~~Home Manager's flake.lock is currently too out of date for this. #7273~~

Because of how Anki's configuration is stored, I was not able to add anything like extraConfig. That's why there are so many options. I've used official Anki APIs wherever possible to prevent breakage; it has worked for many months for me without issue.

Addons added with programs.anki.addons don't seem to show up when Anki is built via tests but do in normal usage. I'm not sure why.

Checklist

• [x] Change is backwards compatible.

• [x] Code formatted with nix fmt or nix-shell -p treefmt nixfmt-rfc-style keep-sorted --run treefmt.

• [x] Code tested through nix-shell --pure tests -A run.all or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes.

• [x] Test cases updated/added. See example.

• [x] Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • [x] Added myself as module maintainer. See example.

Maintainer CC