refactor(nix)!: move nix module to programs

modules/programs/nix.nix

@@ -0,0 +1,66 @@
+{ config
+, lib
+, inputs
+, ...
+}:
+
+with lib;
+let
+  cfg = config.my.programs.nix;
+in
+{
+  options.my.programs.nix = {
+    gc = {
+      enable = mkEnableOption "nix-gc";
+      minimumFreedGB = mkOption {
+        default = 32;
+        type = types.int;
+        apply = number: toString (number * 1024 * 1024 * 1024);
+      };
+    };
+    optimise.enable = mkEnableOption "nix-optimise";
+  };
+
+  config.nix = {
+    gc = {
+      automatic = cfg.gc.enable;
+      options = "--max-freed ${cfg.gc.minimumFreedGB} --delete-older-than 14d";
+      dates = "weekly";
+    };
+
+    optimise = {
+      automatic = cfg.optimise.enable;
+      dates = [ "weekly" ];
+    };
+
+    registry = {
+      master-upstream.to = {
+        type = "github";
+        owner = "nixos";
+        repo = "nixpkgs";
+      };
+      master.flake = inputs.master;
+      nixpkgs.flake = inputs.nixpkgs;
+      stable.flake = inputs.stable;
+    };
+
+    settings = {
+      substituters = [
+        "https://cache.nixos.org/"
+        "https://jupyterwith.cachix.org"
+        "https://nix-community.cachix.org"
+        "https://pre-commit-hooks.cachix.org"
+        "https://hyprland.cachix.org"
+      ];
+      trusted-public-keys = [
+        "jupyterwith.cachix.org-1:/kDy2B6YEhXGJuNguG1qyqIodMyO4w8KwWH4/vAc7CI="
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+        "pre-commit-hooks.cachix.org-1:Pkk3Panw5AW24TOv6kz3PvLhlH8puAsJTBbOPmBo7Rc="
+        "hyprland.cachix.org-1:a7pgxzMz7+chwVL3/pzj6jIBMioiJM7ypFP8PwtkuGc="
+      ];
+
+      trusted-users = [ "root" "@wheel" ];
+    };
+  };
+}