package pa'i as a flake

[oldaccountdeadname]

Hi - this fork replaces the current Nix/Niv build system with Nix Flakes. Some questions that are unresolved:

• Should the current Niv setup be kept alongside the Flakes solution? If so, can the current expressions be reused to any extent?
• Should the 'internal' dependencies --- docs/, olin-spec/, etc --- have their default.nix's either renamed or redone for consistency?
• How should I go about supporting non-linux-x86_64 platforms? The flake.nix build expression only has an ouptut for that, which is intentional: I've tested Pa'i with nothing else. I've not got machines running anything else on bare metal, nor do I have any experience with virtualization, so I'm a bit lost here.
• And, of course, is it valuable to have this available as a Flake? I found this to be convenient for some of my experimentation, but I know nothing :))

[oldaccountdeadname]

Pure evaluation is almost there. The branch pure of my fork overrides Olin with my fork which does support pure evals, and the PR for that is mentioned in that last commit message. Other than that, the flake is kind of a mess and I will get to cleaning it up :sparkles: soon! :sparkles: