Right now since the repo is having two different implementations of
codex, flake was updated to work with both typescript implementation and
rust implementation
This PR introduces a Nix flake configuration to enable reproducible
development environments:
- Adds flake.nix defining a devShell with necessary dependencies.
- Updates README.md with usage instructions for `nix develop`.
- Ensures CI compatibility with Nix for consistent builds.
Jörg Thalheim