Create a sandbox environment for experimentation

[leouieda]

Set up a nox session that just installs all dependencies plus some extras (jupyter et al) in a conda environment. It can activated with conda activate .nox/sandbox and should serve to run individual scripts, prototype new features in jupyter, etc.

Reminders:

• [ ] Run make format and make check to make sure the code follows the style guide.
• [ ] Add tests for new features or tests that would have caught the bug that you're fixing.
• [ ] Add new public functions/methods/classes to doc/api/index.rst and the base __init__.py file for the package.
• [ ] Write detailed docstrings for all functions/classes/methods. It often helps to design better code if you write the docstrings first.
• [ ] If adding new functionality, add an example to the docstring, gallery, and/or tutorials.
• [ ] Add your full name, affiliation, and ORCID (optional) to the AUTHORS.md file (if you haven't already) in case you'd like to be listed as an author on the Zenodo archive of the next release.

[leouieda]

I changed it to sandbox-boule so that all commands start with sandbox. The one thing is that the environment name is tied to the nox session name. So you have to run nox -s sandbox-boule. But it's not a huge problem, I guess.