Don't look for NixOS options when module-list.nix or lib doesn't exist

[figsoda]

so nil doesn't output an error when with something like this: inputs.nixpkgs.url = "github:nix-community/nixpkgs.lib";

[oxalica]

Could we rely on the .version file? Seems lib.trivial.release is just reading this file.

[figsoda]

To replace builtins.compareVersions trivial.release "22.11" >= 0? I would say yes

Though this wouldn't be the only thing I rely on since it is a popular file name: https://github.com/search?q=path%3A%2F%5E%5C.version%24%2F&type=code
I think having both .version and nixos/modules/module-list.nix would be a fairly safe bet

[oxalica]

I also made the input name of nixpkgs used for options configurable in 21d0870