Migration to flake

[AlexSherbinin]

• Introduced Rust build support using Nix's flake.
• Implemented checks for stable, beta, and nightly toolchain channels. These checks include: cargo-nextest for parallel testing (replacing cargo test), clippy for linting, and fmt for formatting check.
• Added a CI workflow to update the Rust version in flake.lock.

[igordejanovic]

Thanks. I tried this config today and just can't get it to work. Please see nix-build branch. Command nix flake check runs very long time. Actually, couldn't wait for it to finish. It looked like it was running in infinite loop.

Could you take a look?

[igordejanovic]

Ah, I figured out that all tests are run for each package (nix flake check -L), that's why it takes extremely long.

[igordejanovic]

I think I've resolved all issues. Now, a single derivation with dependencies is built per workspaces, sources are cleaned properly and only one check is done per toolchain/workspace. We could probably optimize the CI pipeline further but it finish in reasonable time. I would also like to add code coverage and advisory-db check but I think that would be now much easier to do.

Thanks for the contribution.