chore(deps, ci): Updates nyc and moves to Codecov

[jbottigliero]

We dropped pushing updates to Coveralls from CI when we moved to GitHub actions. It looks like most of the org is using Codecov as we no longer have Coveralls configured.

• Removes coveralls integration.
• Updates GitHub actions to include CodeCov step.
• Moves OS to strategy matrix – we're now testing across multiple versions of Windows.
• Related dependency bumps.

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• Once merged we'll need to update required status checks to reflect the new matrix.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@f158d6f). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #701   +/-   ##
=========================================
  Coverage          ?   97.71%           
=========================================
  Files             ?       24           
  Lines             ?     1051           
  Branches          ?        0           
=========================================
  Hits              ?     1027           
  Misses            ?       24           
  Partials          ?        0           

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