e893346d

Your first flake

Adds a `flake.nix` so the project can be built and checked with Nix (and run on NixCI).

It provides:

* `packages.default` — builds the dspy wheel (`python -m build`).
* `devShells.default` — python + uv + ruff + pre-commit development environment.
* `checks` — the package, the devShell, and a ruff lint gate mirroring the existing CI.

`nix flake check` builds every package and devShell.

Passing CI: https://staging.nix-ci.com/gh:NorfairKing:dspy/your-first-flake/cb8190b66789cb31dcb8babd71f9006186d44c65