Some improvements to CI setup

[giordano]

• address post-merge review in test: use ParallelTestRunner #2310 (comment)
  • make tests more verbose
  • make macOS jobs actually parallel
• guard test filtering with filter_tests!
• use earlyoom to better handle out-of-memory situations

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.66%. Comparing base (b39a1fc) to head (ce83339).
⚠️ Report is 586 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (b39a1fc) and HEAD (ce83339). Click for more details.

HEAD has 9 uploads less than BASE

Flag	BASE (b39a1fc)	HEAD (ce83339)
	99	90

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2369       +/-   ##
===========================================
- Coverage   68.16%   36.66%   -31.50%     
===========================================
  Files         109      195       +86     
  Lines       11779    28306    +16527     
===========================================
+ Hits         8029    10379     +2350     
- Misses       3750    17927    +14177     

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[giordano]

This is ready for review.