Home Manager's Linux Submodules

1. base: The base module that is suitable for any NixOS environment.
2. desktop: Configuration for desktop environments, such as Hyprland, I3, etc.
3. server.nix: Configuration which is suitable for both servers and desktops. It import only base as its submodule.
   1. used by all my nixos servers.
4. desktop.nix: the entrypoint of desktop's configuration, it import both base and desktop as its submodules.
   1. used by all my nixos desktops.