newt, python3Packages.snack: fix darwin linking

[bryango]

The python module "snack" (packaged along with "newt") has been failing on darwin (the job succeeds but the python c extension fails to be built and is simply absent). This causes commands that relies on python3Packages.snack to fail, e.g. byobu-config from the byobu package.

This patch uses some linker magic borrowed from

nixpkgs/pkgs/by-name/sp/spade/package.nix

Line 55 in f61bd35

env.NIX_CFLAGS_LINK = lib.optionalString stdenv.hostPlatform.isDarwin "-L${python312}/lib/python3.12/config-3.12-darwin -lpython3.12";

to fix the issue.

This patch only changes the derivation hash on darwin; it should cause zero rebuild on linux. There are 3 commits:

1. move to by-name and adopt the package
2. clean up and explicitly add gettext for clang on darwin
3. fix python module (c extensions) with some linker magic
4. (new) add a (nonblocking) pythonImportsCheck to passthru.tests
5. (new) fix up the dylib names in _snack (bug revealed by the previous test)

Things done

• 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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[bryango]

--disable-nls can be removed now as the required gettext is added for darwin.