also refactor nixos modules

modules/nixos/nix.nix

@@ -0,0 +1,43 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}: let
+  cfg = config.sneeuwvlok.nix;
+in {
+  options.sneeuwvlok.nix = {};
+
+  config = {
+    programs.git.enable = true;
+
+    nix = {
+      package = pkgs.nixVersions.latest;
+
+      extraOptions = "experimental-features = nix-command flakes pipe-operators";
+
+      settings = {
+        experimental-features = ["nix-command" "flakes" "pipe-operators"];
+        allowed-users = ["@wheel"];
+        trusted-users = ["@wheel"];
+
+        auto-optimise-store = true;
+        connect-timeout = 5;
+        http-connections = 50;
+        log-lines = 50; # more log lines in case of error
+        min-free = 1 * (1024 * 1024 * 1024); # GiB # start garbage collector
+        max-free = 50 * (1024 * 1024 * 1024); # GiB # until
+        warn-dirty = false;
+      };
+
+      gc = {
+        automatic = true;
+        dates = "monthly";
+        options = "--delete-older-than 45d";
+      };
+
+      # disable nix-channel, we use flakes instead.
+      channel.enable = false;
+    };
+  };
+}