nix builds on CI failing

[cqc-alec]

Seems they aren't using the latest version of mypy.

[jake-arkinstall]

I've wanted to do a nix flake update for a while so that should fix it.

Do you have a preference as to which python version should be the default when built with nix?

[jake-arkinstall]

Which mypy version is required? Is this documented anywhere?

The version provided by the latest nixpkgs revision is 1.11.2, and the test still fails on that. Pypi has 1.13, so I'll grab the original nixpkgs src and modify it to use that version.

[cqc-alec]

I've wanted to do a nix flake update for a while so that should fix it.

Do you have a preference as to which python version should be the default when built with nix?

No particular preference, maybe 3.12 would be safest?

The mypy version used is always the latest on pipy, currently 1.13.0.