Haumea integration

[figsoda]

https://github.com/oxalica/nil/commit/5b99f7aab5d2ed11ddd83fbd882a26196d96886a added completions for NixOS Options, it would be nice if this feature would work with NixOS modules loaded with haumea

Some notable differences are:

• The top level lambda parameters doesn't need to have ...
• Content of the files are relative to the file path, so for src/nix.nix, the contents of the file would be within nix: { nix = { /* contents */ }; }

This can be discovered if the module is a lambda that calls haumea.lib.load, and the files would be relative to src: https://github.com/figsoda/cfg/blob/5d10ef36cefb3b36eb529df5a34f106c2cb4965d/flake.nix#L27

[oxalica]

Not a fan of supporting any custom library APIs, unless they are somehow endorsed by upstream (NixOS/nix or NixOS/rfcs). There are too many libraries.

[figsoda]

guess I'll wait for cross file analysis and more eval