CI pre-commit check

[calumy]

Type of changes

• [ ] Bug fix
• [ ] New feature
• [ ] Documentation / docstrings
• [ ] Tests
• [x] Other (CI)

Checklist

• [x] I've run the latest black with default args on new code.
• [ ] I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• [ ] I've added tests for new code.
• [x] I accept that @willmcgugan may be pedantic in the code review.

Description

The contributing guidelines suggest that pre-commit should be used when committing (Contributing/pre-commit). This PR adds a workflow to run pre-commit for all files for each PR. It also updates instances where pre-commit has not been run before committing (mainly end of file fixes and isort) so that the workflow will initially pass.