Add unbounded queue

[alesr]

Extend worker pool with support for unbounded queues via options, and split implementation for readability.

[codecov]

Codecov Report

❌ Patch coverage is 86.71875% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.85%. Comparing base (781a462) to head (44c3897).

Files with missing lines	Patch %	Lines
unboundedpool.go	80.76%	15 Missing ⚠️
boundedpool.go	94.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
+ Coverage   83.01%   87.85%   +4.83%     
==========================================
  Files           1        3       +2     
  Lines          53      140      +87     
==========================================
+ Hits           44      123      +79     
- Misses          8       17       +9     
+ Partials        1        0       -1     

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