Draft: project: Use last black for new commits

This MR uses conda to provide dev libraries.

As result the last black is used.

As the CI style checker only tests edited files, old blackified files can stay in the repository, until somebody touch it.

So if this proposal is merged, you have to update you dev libs:

conda install --file requirements-dev-conda.txt

This MR includes blackified flint source, in order to test the CI.