Miscellaneous code quality improvements

[henrymercer]

Enable some more ESLint rules to improve code quality going forwards.

Merge / deployment checklist

• [ ] Confirm this change is backwards compatible with existing workflows.
• [ ] Confirm the readme has been updated if necessary.
• [ ] Confirm the changelog has been updated if necessary.

[github-actions[bot]]

Pushed a commit to update the checked-in dependencies. Please mark the PR as ready for review to trigger PR checks.