Support for Python 3.10

[Dapid]

Description

Now it works under Python 3.10

Key checklist:

• [ x] No style issues: $ flake8
• [ x] All tests pass: $ python run-tests.py --unit
• [ x] The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

N/A

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[brosaplanella]

Hi! Thanks for the contribution, unfortunately we can't support Python 3.10 yet as a main dependency (CasADI) does not support it. We already have #2435 in progress for when CasADI updates.

If you want to contribute to PyBaMM a good place to start are the issues labelled as easy.