Update to Python 3.10

[BenWinchester]

Issue

Python 3.7, currently used throughout CLOVER, will cease being support from June 2023. As such, there is a need to transfer to a newer version of Python.

Proposal

Python will be upgrade throughout CLOVER from version 3.7 to 3.10. This will result in:

• Cosmetic changes to the code to utilise some of the 3.10 functionality,
• Changes to the mypy, pylint, black and yamllint ✨ linters ✨ that are run on CLOVER,
• Changes to some of the unit testing.

In terms of alternatives, there are versions 3.8, 3.9 and, potentially, 3.11. 3.8 and 3.9 will suffer from the same issue as 3.7, and simply create more work. 3.11 will be used if it is released.