Prefer `require_relative` for internal requires

[tagliala]

require_relative is preferred over require for files within the same project because it uses paths relative to the current file, making code more portable and less dependent on the load path.

This change updates internal requires to use require_relative for consistency, performance, and improved portability.

However, the test directory makes an exception and there require is preferred

Fix Packaging/RequireRelativeHardcodingLib safe offense

Ref:

• ruby/psych#522
• ruby/logger#20
• ruby/rdoc#658
• rubocop/rubocop#8748
• https://docs.rubocop.org/rubocop-packaging/cops_packaging.html#packagingrequirerelativehardcodinglib

[tagliala]

@jamesmartin and ready for review

Then I will go for another round of RuboCop offenses

[tagliala]

Sorry, I forgot to remove draft

[jamesmartin]

Thanks, @tagliala! 🙇