Generate pytestCheckHook input and usage in nativeCheckInputs if you detect a pytest dependency.

[zmitchell]

I recently used nix-init to package someone else's Python package and it was so, so nice. The only thing that it didn't really generate for me was the need to use pytestCheckHook to run the package's test suite. It seems like it would be possible to parse a requirements.txt or pyproject.toml to look for a pytest dependency and then generate the necessary code to automatically run the package's test suite.