laptop: check for tuned service before enabling tlp

[JoaquinTrinanes]

Description of changes

This PR adds an extra check to the logic that conditionally enabled tlp on laptops by default. Before, it was enabled if power-profiles-daemon.

With this change, we also check for services.tuned.enable, which also conflicts with tlp. Enabling tuned and loading the default laptop module resulted in an evaluation error of the config.

I have a couple of questions regarding the changes:

• Looking at the NixOS tuneD module, auto-cpufreq also conflicts with the service. Should we add a check for it as well?
• The original logic used a lib.version check before accessing the power-profiles-daemon to avoid evaluation error in older NixOS releases (pc/laptop: fix evaluation on 20.09 #270). I replaced that with an existence check for both options for consistency, but I can revert that part (tuned was released in 25.05 I believe).

In the end, this PR is superseded by #1474, but it is a nice QOL improvement while it doesn't land.

Things done

• Tested the changes in your own NixOS Configuration
• Tested the changes end-to-end by using your fork of nixos-hardware and
  importing it via <nixos-hardware> or Flake input

[trueNAHO]

• Looking at the NixOS tuneD module, auto-cpufreq also conflicts with the service. Should we add a check for it as well?

I am using /common/pc/laptop/default.nix and enable services.auto-cpufreq.enable, resulting in service.tlp.enable being implicitly enabled.

Although both services may conflict, they can apparently be used together. Personally, I just keep both enabled without bothering with fancy configurations on my end, hoping auto-cpufreq works reasonably well alongside tlp. Either way, my system never crashed due to this, if that is of interest.

Consequently, I do not know whether a warning or assertion would be appropriate.