feat(pool): add support for dynamically adjusting max concurrency

[alitto]

Add support for dynamically adjusting the maximum concurrency of the pool (number of workers) via a new method Resize(maxWorkers int)

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.62%. Comparing base (e2470f0) to head (bbe9b32).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pool.go	95.45%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
- Coverage   94.62%   94.62%   -0.01%     
==========================================
  Files          11       11              
  Lines         688      725      +37     
==========================================
+ Hits          651      686      +35     
- Misses         34       35       +1     
- Partials        3        4       +1     

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