Changes proposed in this PR:

• Make all the centroids data to be stored in a geodataframe attribute
• Removes and simplifies a lot of the methods.

This is a DRAFT, and comments are welcome. Not all tests are already running through as many tests are using the centroids class even though they should not. But this will be fixed once we converge to a final result.

This pull request is getting close to review-ready, pending some open discussion points (see below).

PR Author Checklist

• Read the Contribution Guide
• Correct target branch selected (if unsure, select develop)
• Descriptive pull request title added
• Source branch up-to-date with target branch
• Documentation updated
• Tests updated
• Tests passing
• No new linter issues
• Changelog updated

PR Reviewer Checklist

• Read the Contribution Guide
• CLIMADA Reviewer Checklist passed
• Tests passing
• No new linter issues