* Bump to arkworks-0.4.0

* Replace remaining usages of `msm_bigint` with `msm_unchecked`

Using `msm_unchecked` instead of `msm_bigint` allows to delete the BigInt conversion code by letting the library take care of it.

* update nix to flake

* add nix sanity check cronjob

- add mock circuits
- add vanilla and jellyfish plonk gates
- performance tuning