Run Saffron in it's own workflow, restore OG CI for core lib only

[martyall]

This actually fixes the problem that #3023 failed to address.

• Run all saffron unit tests in their own workflow
• Stop running saffron in the general CI workflow

Post Mortem

The tests themselves weren't even the problem -- there were 2 other major factors:

• The code coverage job was building everything with instrumentation flags that were causing something like a 100x slowdown 🤯
• Since the tests were being run without the SRS cache, they were spending a lot of time computing one (likely once per test module)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.23%. Comparing base (1569ce6) to head (a40d707).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3035      +/-   ##
==========================================
+ Coverage   76.89%   77.23%   +0.34%     
==========================================
  Files         262      254       -8     
  Lines       62118    61044    -1074     
==========================================
- Hits        47763    47150     -613     
+ Misses      14355    13894     -461     

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[dannywillems]

LGTM. I checked it was not running the Saffron tests.