attempt switch from nyc to c8

[cspotcode]

I've done a bunch of nyc support hacks in our tests, and yet there are still weird issues.

I'm hopeful that switching to c8 avoids all that.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.49%. Comparing base (97f9afd) to head (c090710).
⚠️ Report is 30 commits behind head on main.

Additional details and impacted files

see 46 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.