Remove Codecov Cache as we might be exceeding Github Limits

[mborland]

Also adds a runner for reverse mode autodiff coverage @demroz

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.24%. Comparing base (758a9fc) to head (c53d28c).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1320      +/-   ##
===========================================
+ Coverage    95.11%   95.24%   +0.13%     
===========================================
  Files          797      814      +17     
  Lines        67197    69309    +2112     
===========================================
+ Hits         63912    66015    +2103     
- Misses        3285     3294       +9     

see 20 files with indirect coverage changes

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