[tests env] swtich from pipenv to uv to handle python dependencies for tests

[cderv]

uv is the new kid around about package management https://docs.astral.sh/uv

it recently added a lock file that is cross OS uv.lock. This is not something we have with pipenv and it created issue recently (we needed to pin pipenv #11263)

This should solve the problem, and uv is really fast !! So it could also maybe make our workflow faster.

This is PR is a first try at a switch to manage the project virtualenv in tests/.venv using uv on CI.

I tested everything locally too, as I relied on pipenv myself. I don't know how the rest of the team is managing the python environment for tests, but this should make it a lot easier.

Once uv is installed on the system it is a matter of

cd tests/
uv sync

This

• Download the right python version for the project
• creates the virtualenv or update the virtualenv
• install dependencies per the lock file.

Then uv helps in upgrading dependencies, and adding one (stored in pyproject.toml

Let's see if this helps.

Aims is also to see if Quarto 1.6 does works correctly with latest Python tooling.