[Chore] Add weeder check

[Sereja313]

Problem: We want to be able to check our Haskell applications for dead code. This can be done using weeder.

Solution: Add weeder check to our overlay.

[rvem]

In fact, it is actually a flake :pled:
Sadly, it doesn't expose executable

[gromakovsky]

Sorry for late review, but recently there appeared https://github.com/NorfairKing/weeder-nix which is now mentioned in https://github.com/ocharles/weeder README. Can we use it to simplify the code written in this PR?

[gromakovsky]

@Sereja313 or @rvem could you please look into it? ⬆️

[Sereja313]

Sorry for late review, but recently there appeared https://github.com/NorfairKing/weeder-nix which is now mentioned in https://github.com/ocharles/weeder README. Can we use it to simplify the code written in this PR?

The current solution is based on the haskell.nix, which we already use for building and testing package, and weeder-nix uses the nixpkgs toolkit to generate hie files. So I'm guessing there may be inconsistencies when the package builds with haskell.nix, but it also requires some manual work to make it suitable for building with nixpkgs to get weeder-nix to work.
So I'm not sure if it's worth it