Multi-dimensional learning rate (sigma0) for AdamW

[BradyPlanden]

Description

Adds multi-dimensional sigma0 values to AdamW, updates integration tests for multi-dimensional sigma0, and updates the default value in GaussianLogLikehood sigma0

Issue reference

Fixes #461

Review

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.03%. Comparing base (76de36a) to head (20b62ed).
Report is 28 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #462      +/-   ##
===========================================
- Coverage    99.04%   99.03%   -0.01%     
===========================================
  Files           52       52              
  Lines         3545     3527      -18     
===========================================
- Hits          3511     3493      -18     
  Misses          34       34              

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[martinjrobins]

looks good to me. I see that you fixed a few of the cost funtions gradient calculations as well