chore: Simplify main function by extracting new functions and adding tests

[zkoppert]

Pull Request

related to #91 but more work to be done to mark as completed

Proposed Changes

This pull request refactors the cleanowners.py script and adds new test cases to improve code maintainability and test coverage. The main changes include extracting the logic for fetching the CODEOWNERS file into a separate function and adding functions for printing statistics and writing reports. Corresponding unit tests have been added to ensure the new functions work correctly.

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing
• If publishing new data to the public (scorecards, security scan results, code quality results, live dashboards, etc.), please request review from @jeffrey-luszcz

Reviewer

• Label as either fix, documentation, enhancement, infrastructure, maintenance or breaking