nix-init: refactor with nixfmt-rfc-style, passthru.tests.version and removing darwin sdk

[kachick]

Things done

> nix-build --attr pkgs.nix-init.passthru.tests     
this derivation will be built:
  /nix/store/54850gkq3dm8rmva6d14cjlw2gkw0g0d-nix-init-0.3.2-test-version.drv
this path will be fetched (6.46 MiB download, 18.98 MiB unpacked):
  /nix/store/d371fzmyvnssxkgf1r1vqg47fd8y63i0-nix-init-0.3.2
copying path '/nix/store/d371fzmyvnssxkgf1r1vqg47fd8y63i0-nix-init-0.3.2' from 'https://cache.nixos.org'...
building '/nix/store/54850gkq3dm8rmva6d14cjlw2gkw0g0d-nix-init-0.3.2-test-version.drv'...
nix-init 0.3.2
/nix/store/j6ln6ysgqv4kyliq7m40llrglp5layqg-nix-init-0.3.2-test-version

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[uncenter]

(You could probably amend that last commit into nix-init: remove unnecessary darwin sdk commit if you want :p)

[kachick]

Thank you for reviewing! Now rebuilding the nixpkgs-review again, I'll post the result after finish 🙏

[uncenter]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 356985

---

aarch64-darwin

✅ 1 package built:

• nix-init

[kachick]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 356985

---

x86_64-linux

---

x86_64-darwin

✅ 1 package built:

• nix-init

---

aarch64-darwin

✅ 1 package built:

• nix-init

[Aleksanaa]

@ofborg build nix-init

[kachick]

Thanks for your reviews!