Implement sliding window circuit breakers

[cinar]

This PR implements sliding window circuit breakers with both count-based and time-based strategies as requested in issue #33.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.08176% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.19%. Comparing base (48a0c4e) to head (4ef5c2e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
circuit/breaker.go	93.03%	6 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
+ Coverage   81.11%   83.19%   +2.07%     
==========================================
  Files          12       12              
  Lines         715      851     +136     
==========================================
+ Hits          580      708     +128     
- Misses        111      115       +4     
- Partials       24       28       +4     

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