Add PRO metric

[djdameln]

Description

This PR adds the PRO metric, and speeds up AUPRO computation when on cpu.

• Add PRO metric
• Add alternative connected component computation method to speed up evaluation on CPU.

Changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which refactors the code base)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the pre-commit style and check guidelines of this project.
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes

[ashwinvaidya17]

I am not very familiar with this technique so I didn't understand some parts of it but other than that the PR looks good. Thanks!

[samet-akcay]

Thanks, only 2 minor comments.

[djdameln]

@samet-akcay I didn't realize this PR was still open. I just addressed your comments. Could you do another round of review?

[samet-akcay]

looking good 🔥, thanks