`eval-config.nix` will set the canonical path for us that will then be used
to strip the module path prefixes in `nixos/modules/misc/documentation.nix` [1].
This should fix split docs build problems described in #50.
[1] 1511e72b75/nixos/modules/misc/documentation.nix (L79)
Allow flake users to import .#nixosModules.deploymentOptions
into their flake, so that the same expression can be used for both,
.#colmena.$host as well as .#nixosConfiguration.$host, without the
latter complaining about undefined options in "deployment".
This decouples expression generation from evaluation. `NixExpression`s
that evaluate to a set of derivations can be fed to `DrvSetEvaluator`s
which may be able to parallelize evaluation.
This partially addresses #33, and allows Colmena to be used more
easily on bandwidth-constrained hosts and macOS.
With `deployment.buildOnTarget = true;` deployment works fine from
macOS without designated builders, except when IFD is involved.
This makes evaluation faster especially when `nodes` is heavily used in
the configuration (like in my auto-meshing setup). This matches the
behavior of Morph.
