Add an action for CodeCov

[everettraven]

Proposed Changes

add a GitHub Actions workflow for getting code coverage reports and uploading them to CodeCov.

Type of Change

What kind of change to packageless is this?

• Bug Fix
• Feature
• Documentation
• Repository Enhancement
• Testing

Checklist

Before the Pull Request can be considered for merging, the following Checklist should have the corresponding fields completed:

• All tests have passed locally after running go test ./...
• I have added tests that prove my fix or feature works as expected
• I have added any necessary documentation for my fix or feature

Comments

Any further information you want to provide can go here.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (main@70c3a61). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #71   +/-   ##
=======================================
  Coverage        ?   88.40%           
=======================================
  Files           ?        7           
  Lines           ?      716           
  Branches        ?        0           
=======================================
  Hits            ?      633           
  Misses          ?       55           
  Partials        ?       28           

Flag	Coverage Δ
subcommands-coverage	88.40% <0.00%> (?)

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