feat: add host 'nixos-unstable' as a testing VM

hosts/nixos-unstable/configuration.nix

@@ -0,0 +1,47 @@
+{ config, lib, pkgs, ... }:
+
+{
+  # Use the systemd-boot EFI boot loader.
+  boot.loader.systemd-boot.enable = true;
+  boot.loader.efi.canTouchEfiVariables = true;
+
+  # Use latest kernel.
+  boot.kernelPackages = pkgs.linuxPackages_latest;
+
+  networking.hostName = "nixos-unstable"; # Define your hostname.
+
+  # Set your time zone.
+  time.timeZone = "Europe/Amsterdam";
+
+  # Select internationalisation properties.
+  # i18n.defaultLocale = "en_US.UTF-8";
+  # console = {
+  #   font = "Lat2-Terminus16";
+  #   keyMap = "us";
+  #   useXkbConfig = true; # use xkb.options in tty.
+  # };
+
+  # Define a user account. Don't forget to set a password with ‘passwd’.
+  users.mutableUsers = false;
+  users.users.root.hashedPassword = "$y$j9T$i4Yx7PqpLH9bPaNb4SVLm/$dv2gVHCHiRZv.Y00rbNx4QeIExunnfHp57WEnh8qLF1";
+  users.users.alice = {
+    isNormalUser = true;
+    hashedPassword = "";
+    extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
+    packages = with pkgs; [
+      tree
+    ];
+  };
+
+  environment.systemPackages = with pkgs; [
+  ];
+
+  # Open ports in the firewall.
+  # networking.firewall.allowedTCPPorts = [ ... ];
+  # networking.firewall.allowedUDPPorts = [ ... ];
+  # Or disable the firewall altogether.
+  # networking.firewall.enable = false;
+
+  system.stateVersion = "25.05"; # Did you read the comment?
+
+}