Add codecov settings

[edabor]

Add codecov settings (copy-paste from pyvista)

To be fair the codecov comment gave misleading checkmarks of approval ✅. I think project settings are the problem for not enforcing this and making coverage thresholds a requirement.

We lost coverage before too: #196 (comment)

Which I believe was fixed by #202. Might be helpful for fixing the issue here too.

Originally posted by @user27182 in #271 (comment)

[edabor]

Instead of duplicating codecov settings all over the place, we could also set a global yaml for all repos in the pyvista organization here

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.68%. Comparing base (063a3f9) to head (ba1f801).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #279   +/-   ##
=======================================
  Coverage   96.68%   96.68%           
=======================================
  Files           4        4           
  Lines         965      965           
  Branches      123      123           
=======================================
  Hits          933      933           
  Misses         24       24           
  Partials        8        8           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[banesullivan]

Instead of duplicating codecov settings all over the place, we could also set a global yaml for all repos in the pyvista organization here

This is neat! However, I'd prefer our configuration as code be checked into a reposiotry somewhere as opposed to on codecov's web platform. Otherwise I will 100% forget where it is configured and be very confused when it automatically applies to some other repo in the org