add code coverage to CI

[lkeegan]

• add pytest-cov to conda environment
• generate code coverage report when pytest runs in CI
• upload report to codecov.io

Next step: go to https://github.com/apps/codecov and enable codecov integration for this repository to see coverage reports on github PRs

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (dev-ssciwr@1a3f1a9). Click here to learn what that means. The diff coverage is n/a.

@@              Coverage Diff              @@
##             dev-ssciwr     #116   +/-   ##
=============================================
  Coverage              ?   10.31%           
=============================================
  Files                 ?       36           
  Lines                 ?     4188           
  Branches              ?        0           
=============================================
  Hits                  ?      432           
  Misses                ?     3756           
  Partials              ?        0           

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