nix: Package zerofs in nix, add nixos module, and nixos tests

[hinshun]

Hi @Barre, not sure if there's appetite to have Nix support but I'd like to use ZeroFS in my NixOS fleet. I packaged zerofs in Nix, added NixOS modules which provides the systemd services for NixOS and I've also added integration tests using NixOS's qemu VM test harness that you can run locally and even breakpoint inside with machine.shell_interact().

Perhaps it's an improvement over the integration tests you're maintaining in github actions atm. See how they're used here in nix-snapshotter: https://github.com/pdtpartners/nix-snapshotter/blob/ce7698e34990e1e59b9693e5c8ec08f4d9bf2fb6/.github/workflows/ci.yml#L40 and https://github.com/pdtpartners/nix-snapshotter/tree/main/modules/nixos/tests.

If you have nix installed, you can run the tests with: nix run .#test-nfs, nix run .#test-nbd-zfs, etc. You could also get caching via cachix, etc.

[vercel]

@hinshun is attempting to deploy a commit to the Pierre Barre's projects Team on Vercel.

A member of the Team first needs to authorize it.

[cla-assistant]

All committers have signed the CLA.

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Barre]

Hi,

Thank you for the contribution!

Hi @Barre, not sure if there's appetite to have Nix support but I'd like to use ZeroFS in my NixOS fleet.

I'd like to have such support, I am not a Nix user myself, so I'll need a bit of time to review this properly.

[dcdq]

This is fantastic, thank you. Would definitely urge adopting more nix on top of this pr for zerofs development and cicd.