Refactor/initial rubocop rework

[luke-hill]

Description

Begin to standardise all of the rubocop tech debt we have, with a few to starting to click off a few of the easy wins later on in v9.0.x

Type of change

Please delete options that are not relevant.

• Refactoring (improvements to code design or tooling that don't change behaviour)
• If your change may impact future contributors, explain it here, and remember to update README.md and CONTRIBUTING.md accordingly.

Please add an entry to the relevant section of CHANGELOG.md as part of this pull request.

Checklist:

Your PR is ready for review once the following checklist is
complete. You can also add some checks if you want to.

• Tests have been added for any changes to behaviour of the code
• New and existing tests are passing locally and on CI
• bundle exec rubocop reports no offenses
• RDoc comments have been updated
• CHANGELOG.md has been updated