Upgrade to Django 4.2.x and Python 3.12.x

[stevejalim]

This changeset moves Nucleus up to Python and Django versions that are not too close to EOL.

The move to Python 3.12.1 also meant moving away from gunicorn+meinheld, as meinheld won't compile above Python 3.9

While in the neighbourhood, I've also switched to ruff from isort + flake8

To test:

• check out branch
• make clean build test
• docker-compose up web
• make run-shell then ./manage.py createsuperuser to be able to log in
• Go to http://localhost:8000 and log in to the nucleus admin
• add a release or two, with some notes to confirm all works ok

Other considerations:

• We can also test this on nucleus dev once it's hit master, but there's no test env. Suggestions/recollections for how this has been tested in the past are welcome.

[robhudson]

r+wc

[robhudson]

Nice 🥳