[ci] add coverage

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@371fffc). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #59   +/-   ##
=========================================
  Coverage          ?   51.96%           
=========================================
  Files             ?       36           
  Lines             ?     3722           
  Branches          ?        0           
=========================================
  Hits              ?     1934           
  Misses            ?     1588           
  Partials          ?      200

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[tmc]

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