Introduce Nix flake for building/running the application via nix.

[svin24]

Add a flake.nix to allow building and running the project with Nix, including a dev shell.

Also includes a check in external/CMakeLists.txt 's corrosion package to allow building with Nix.

Usage:

• Build: nix build
• Run: nix run
• Dev shell: nix develop

originally the flake was pinned but it turned out it didn't need to be.

Tested on fedora with nix (GPU usage on non nixos enabled) and with NixOS

[redstrate]

Thanks for the contribution! However I have one big problem: I don't use Nix!

This means that the flake will eventually drift out-of-date, since I stopped testing other distribution methods other than Flatpak. I also don't want to put you on the hook for updating this for me forever, so is there a benefit to using the flake on NixOS rather than the Flatpak?

Aside from that, I wonder if there's any way to test this on the CI. That way if we do integrate it, then I'll at least know when it blows up.

[svin24]

understandable if you're not willing to adopt it yet. @redstrate
I'm no nix pro myself I just tried to develop my flake for this program and it worked so i decided to make a PR.
I do however recommend adopting the cmake change as it would probably help with packaging in the future in general.

Also something else i noticed while i was poking around... your .gitmodules point to a directory instead of a git repository.
https://github.com/redstrate/Astra/blob/f8c38149d9ff4b47db26d72199103bf2cbb411e5/.gitmodules#L4C1-L6C20

[redstrate]

I do however recommend adopting the cmake change as it would probably help with packaging in the future in general.

I very much would appreciate that, can you create a separate PR for that so you're credited still?

Also something else i noticed while i was poking around... your .gitmodules point to a directory instead of a git repository.

Yeah :/ It doesn't hurt, but it should probably be changed to a proper URL. Feel free to create another PR for that as well.

[svin24]

I closed this because i separated the flake changes in a different branch in my repo.

I'm not gonna make changes to gitmodules because you are probably actively developing and testing that stuff right now. And you don't want to deal with too many weird submodules on git(it sometimes turns into a pain)