NixOs support

[renxida]

This PR makes some adjustments to pyproject.toml and adds a flake.nix such that people on nixos can easily add aider as a package to their config files.

I also had to check in poetry.lock and flake.lock because nix's package management requires locking package versions for poetry.

This should not affect regular pip installs via requirements.txt

[paul-gauthier]

Thanks for putting together this PR. It looks like it radically changes the build process for aider and breaks all the extras. It seems unlikely that this approach will be viable?

[lee-b]

This does not look radical to me, on first glance. poetry.lock should be checked in, for end-user executable projects like aider (but not for libraries that would only be used as sub-dependencies of other projects). The rest, the flake stuff, seems to just use that in a pretty typical way to run the poetry build.

I was reviewing it because I was concerned that the flake would get out of date quickly if not understood and updated as regularly as the pyproject.toml / poetry.lock by aider maintainers, but doesn't really seem to be the case.

LGTM, personally, assuming that the current build issues (playwright) are just it needing a rebase.