nixos/oo7: install oo7-cli and refactor module layout

[HeitorAugustoLN]

Follow-up to #526624, installs oo7-cli that was missing. I also refactored the module layout to make it easier to look at
cc: @salva09

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.
• Follows the automation/AI policy.

[DaRacci]

LGTM.

Is there a standard of using attribute nesting instead of the full dot path declarations, or is that normally left more up to the maintainer ?

[HeitorAugustoLN]

Is there a standard of using attribute nesting instead of the full dot path declarations, or is that normally left more up to the maintainer?

I don't think there is, I personally find it more readable