nixos/nix-optimise: allow dates to be a single line str

      dates = lib.mkOption {

        default = [ "03:45" ];

        type = with lib.types; listOf str;

        apply = lib.toList;

        type = with lib.types; either singleLineStr (listOf str);

        description = ''

          Specification (in the format described by

          {manpage}`systemd.time(7)`) of the time at