Add pre-commit hook for documentation code formatting

[VeckoTheGecko]

There's https://github.com/adamchainz/blacken-docs which supports

```python
```

code blocks, but doesn't support Myst style code blocks and cells. There is an old WIP PR for Myst support though.

I've also asked in the Scientific Python Discord https://discord.com/channels/786703927705862175/1151161614150680586/1538802038475857940 , and have looked in the myst Discord but its not looking promising at the moment.