ci: bump codecov to v4 and set the CODECOV token from the secrets

[bconn98]

See #378 this PR will track progress towards resolving the Codecov job.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.68%. Comparing base (8ab1b34) to head (cf7f162).
Report is 2 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #379      +/-   ##
==========================================
+ Coverage   63.39%   63.68%   +0.29%     
==========================================
  Files          24       25       +1     
  Lines        1557     1567      +10     
==========================================
+ Hits          987      998      +11     
+ Misses        570      569       -1     

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[bconn98]

Closing and merging into #366 as that PR blocks many others with the intent to resolve the CI.