️ Repo: Use local coverage files

Tooling Suggestion Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Both Codecov and our previous provider Coveralls have had intermittent outages that have caused CI issues. We should replace them with a local store of coverage files if at all possible.

Additional Info

No response