cb8190b6

Add a Nix flake

Adds a flake.nix so the project can be built and checked with Nix (and
demoed on NixCI). It provides:

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

`nix flake check` builds every package and devShell.

Agent Instructions

Each run corresponds to one flake attribute. Click a run for its logs and status.

Example: https://staging.nix-ci.com/gh:NorfairKing:dspy/your-first-flake/cb8190b66789cb31dcb8babd71f9006186d44c65/1ff50b60-edb5-4696-bf5c-f72080a17fb8

Wait for suite to complete:

curl --netrc -N https://staging.nix-ci.com/gh:NorfairKing:dspy/your-first-flake/cb8190b66789cb31dcb8babd71f9006186d44c65/wait

This page is also available in machine-friendly formats. Request one with the Accept header:

• curl --netrc -H 'Accept: application/json' https://staging.nix-ci.com/gh:NorfairKing:dspy/your-first-flake/cb8190b66789cb31dcb8babd71f9006186d44c65
• curl --netrc -H 'Accept: text/markdown' https://staging.nix-ci.com/gh:NorfairKing:dspy/your-first-flake/cb8190b66789cb31dcb8babd71f9006186d44c65

For more instructions, fetch https://staging.nix-ci.com/instructions .