fix: Update structure and packaging

[12rambau]

WIP

I'm in the mood these day so I went on a crusade to update packaging of the extention I'm using in my documentation. I love sphinx-contrib email so I'm taking the time to make few improvement.

I hop you will be interested.

So far this contains:

• drop use of cfg files in favor of only pyproject.toml
• sanytise pre-commits (I think you are using some from another package and many things do were not required (notebooks, html etc) with the combo prettier/ruff/black everythin is covered
• change structure of the files (the src directory is skiped anyway during the build so why keeping it ?
• introduce nox for automated testing (mypy/linting)
• create basic testing (that cover 84% of the code)
• run a unit test on PR and push in github actions