feat(async/unstable): add support for AbortSignal in retry

[tomas-zijdemans]

Sorry, the diff is quite big. I had to bring the unstable code up to speed first.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.25%. Comparing base (c835e4d) to head (f3f5ece).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6938      +/-   ##
==========================================
+ Coverage   94.22%   94.25%   +0.03%     
==========================================
  Files         584      584              
  Lines       43146    43163      +17     
  Branches     6908     6919      +11     
==========================================
+ Hits        40653    40682      +29     
+ Misses       2441     2430      -11     
+ Partials       52       51       -1     

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[kt3k]

LGTM!