I chose not to do nixos.{config, options} because that would make it
look too much like a configuration object, which it is not.
A configuration object I would define as for example the result of
calling NixOS, an attrset with `_type = "configuration";`.
Recreating a configuration object without evalModules is quite
feasible but not guaranteed to be correct, and not maintainable.
This is preferable because it prevents things like disk corruption (requiring the user to delete the disk image when starting up) that I consistently ran into.
See the discussion starting here:
https://github.com/NixOS/nixpkgs/pull/206951#issuecomment-1364760917
The `darwin.builder` derivation had a gratuitous dependency
on the current Nixpkgs revision due to
`config.system.nixos.revision`. Setting the revision explicitly
to null fixes this problem and prevents the derivation from being
rebuilt on every change to Nixpkgs.
See: https://github.com/NixOS/nixpkgs/issues/108984#issuecomment-1364263324
Before this change the supported platforms were unspecified, so
it would default to being only built on `x86_64-linux`. This
fixes that so that hydra.nixos.org builds and caches the Darwin
build products instead
