fix(async/unstable): circuit breaker stale openedAt and duplicate callbacks

[tomas-zijdemans]

• Fix cooldown timer bypassed when wrapped function is slow
• Fix duplicate callbacks on concurrent half-open failures
• Extract tryCall helper to simplify predicate error handling
• Improve JSDoc and add test for synchronous throws

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.42%. Comparing base (a3a6ef6) to head (49a5e7c).

Files with missing lines	Patch %	Lines
async/unstable_circuit_breaker.ts	96.87%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7097      +/-   ##
==========================================
- Coverage   94.43%   94.42%   -0.01%     
==========================================
  Files         630      630              
  Lines       50566    50566              
  Branches     8969     8971       +2     
==========================================
- Hits        47750    47749       -1     
  Misses       2247     2247              
- Partials      569      570       +1     

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