feat: new 'nix' module with some good defaults

modules/nixos/default.nix

@@ -1,4 +1,11 @@
-{ ... }:
+{ lib, ... }:
+let
+  inherit (lib) filterAttrs;
+  inherit (builtins) attrNames readDir;
+  moduleDirs =
+    dir:
+    map (name: dir + "/${name}") (attrNames (filterAttrs (_: type: type == "directory") (readDir dir)));
+in
 {
-
+  imports = moduleDirs ./.;
 }

modules/nixos/nix/default.nix

@@ -0,0 +1,65 @@
+{
+  config,
+  lib,
+  inputs,
+  flake-self,
+  ...
+}:
+let
+  inherit (lib) mkEnableOption mkIf;
+  cfg = config.ataraxia.defaults.nix;
+in
+{
+  options.ataraxia.defaults.nix = {
+    enable = mkEnableOption "Nix defaults";
+  };
+
+  config = mkIf cfg.enable {
+    environment.etc.nixpkgs.source = config.nixpkgs.flake.source;
+    environment.etc.self.source = flake-self.outPath;
+    nix = {
+      channel.enable = false;
+      extraOptions = ''
+        keep-outputs = true
+        keep-derivations = true
+        # Prevent Nix from fetching the registry every time
+        flake-registry = ${inputs.flake-registry}/flake-registry.json
+      '';
+      gc = {
+        automatic = true;
+        dates = "weekly";
+        options = "--delete-older-than 90d";
+      };
+      registry.ataraxia.flake = flake-self;
+      settings = {
+        auto-optimise-store = true;
+        experimental-features = [
+          "nix-command"
+          "flakes"
+        ];
+        require-sigs = true;
+        substituters = [
+          "https://cache.nixos.org"
+          "https://nix-community.cachix.org"
+          "https://hyprland.cachix.org"
+          "https://ataraxiadev-foss.cachix.org"
+          "https://numtide.cachix.org"
+          "https://devenv.cachix.org"
+        ];
+        trusted-public-keys = [
+          "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+          "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+          "hyprland.cachix.org-1:a7pgxzMz7+chwVL3/pzj6jIBMioiJM7ypFP8PwtkuGc="
+          "ataraxiadev-foss.cachix.org-1:ws/jmPRUF5R8TkirnV1b525lP9F/uTBsz2KraV61058="
+          "numtide.cachix.org-1:2ps1kLBUWjxIneOy1Ik6cQjb41X0iXVXeHigGmycPPE="
+          "devenv.cachix.org-1:w1cLUi8dv3hnoSPGAuibQv+f9TZLr6cv/Hm9XgU50cw="
+        ];
+        trusted-users = [
+          "root"
+          "deploy"
+          "@wheel"
+        ];
+      };
+    };
+  };
+}