nixos/switchable-system: add evaluation warning when using perl stc (#350945)

- The Rust rewrite of the `switch-to-configuration` program is now used for system activation by default.

  If you experience any issues, please report them.

  The original Perl script can still be used for now by setting `system.switch.enableNg` to `false`.

  The original Perl script is deprecated and is planned for removal in the 25.05 release. It will remain accessible until then by setting `system.switch.enableNg` to `false`.

- Support for mounting filesystems from block devices protected with [dm-verity](https://docs.kernel.org/admin-guide/device-mapper/verity.html)

  was added through the `boot.initrd.systemd.dmVerity` option.

{ config, lib, pkgs, ... }:

{

  config,

  lib,

  pkgs,

  ...

}:

let

  perlWrapped = pkgs.perl.withPackages (p: with p; [ ConfigIniFiles FileSlurp ]);

  perlWrapped = pkgs.perl.withPackages (

    p: with p; [

      ConfigIniFiles

      FileSlurp

    ]

  );

in

{

  options.system.switch = {

    enable = lib.mkOption {

      type = lib.types.bool;

  config = lib.mkMerge [

    (lib.mkIf (config.system.switch.enable && !config.system.switch.enableNg) {

      warnings = [

        ''

          The Perl implementation of switch-to-configuration will be deprecated

          and removed in the 25.05 release of NixOS. Please migrate to the

          newer implementation by removing `system.switch.enableNg = false`

          from your configuration. If you are unable to migrate due to any

          issues with the new implementation, please create an issue and tag

          the maintainers of `switch-to-configuration-ng`.

        ''

      ];

      system.activatableSystemBuilderCommands = ''

        mkdir $out/bin

        substitute ${./switch-to-configuration.pl} $out/bin/switch-to-configuration \