Switched to `pre-commit.ci`

[davidorme]

Description

This PR removes the pre-commit autoupdate workflow. The repo is now enabled with pre-commit.ci, which tests pre-commit status and provides autoupdate in a more integrated way.

There is some redundancy here - our CI GitHub action already runs pre-commit as part of the qa job, so pre-commit.ci is repeating that on each PR, but the way the autoupdate works is better. See here for the status page:

https://results.pre-commit.ci/repo/github/317618141

And we add a badge to README.md 😄

Since this issue was raised by spotting a failed pre-commit update action, I've also run pre-commit autoupdate and then pre-commit run --all and included those changes to get us back on track. The black tool has changed its mind about a couple of line wrappings and some blank lines 🤷‍♂️

Fixes #217

Type of change

• [ ] New feature (non-breaking change which adds functionality)
• [x] Optimization (back-end change that speeds up the code)
• [ ] Bug fix (non-breaking change which fixes an issue)

Key checklist

• [x] Make sure you've run the pre-commit checks: $ pre-commit run -a
• [x] All tests pass: $ poetry run pytest

Further checks

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

[davidorme]

Adding pyrealm to pre-commit.ci automatically generated PR #221 that basically repeated much of this PR. With that merged to develop and then back into this PR, all that is left is adding the badge and deleting the old GH action file.