refactor(async/unstable): make circuit breaker resilient to throwing callbacks

[tomas-zijdemans]

• fixed a bug where a throwing callback (e.g. onFailure, onStateChange) would crash the circuit breaker mid-update, hiding the original error that your code was trying to throw.
• fixed a bug where failure detection (e.g. flagging HTTP 500 responses as failures) was silently blocked by custom error filters (isFailure), so those results would never trip the circuit breaker
• fixed a bug where two requests racing during recovery could cause a failed request to reopen the circuit, only for a concurrent successful request to immediately close it again.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.20%. Comparing base (1cd85bf) to head (ecdca7f).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6996   +/-   ##
=======================================
  Coverage   94.20%   94.20%           
=======================================
  Files         613      613           
  Lines       47710    47725   +15     
  Branches     8299     8301    +2     
=======================================
+ Hits        44945    44961   +16     
  Misses       2697     2697           
+ Partials       68       67    -1     

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[kt3k]

LGTM