wpaperd: add systemd service; move to services/ from programs/

[3ulalia]

Description

Re: #4538, wpaperd needs something to run it after being enabled. This commit adds a systemd service to run it, and accordingly moves it to services.wpaperd.

In addition, the existing tests have been migrated to services, and an entry in the newslist has been created alerting users to this change.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

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Maintainer CC

@Avimitin

[3ulalia]

CC @thiagokokada

[teto]

I dont have a strong opinion on this but it might make sense to have programs AND service separate in case you want to generate a config without the service. That would be for wpaperd maintainer to decide.

[3ulalia]

I don't know if I agree with that but certainly I'd love to hear from @Avimitin. That doesn't really line up with the way that other programs have been implemented - home-manager is somewhat opinionated whether things should be programs or services.

[Avimitin]

In my previous use case, wpaperd is not usually used as a standalone program. So from my own perspective, for those users who want to use home manager to manage their wpaperd configuration, they might also want the systemd user service installed automatically. So I think having only one service module is ok.

Also, I want to quit the wpaperd maintainer since KDE is now my daily desktop environment. This has nothing to do with this PR, I just want to express that I might miss some new best practices for wpaperd. Please do what you think is right as you see fit.

[3ulalia]

Hello,

That's good to know, and I'd be happy to take up the mantle. I'll go ahead and add myself as a maintainer and remove you, if that works? Thanks for all the work you've done so far!