[#20] MPSC goes to sleep if empty

[maypok86]

Description

When the write buffer is empty, CPU consumption is up to 100%.

Solution: use the standard channel as a sleep marker.

Related issue(s)

#20

✅ Checklist for your Pull Request

Related changes (conditional)

• Tests

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from
    silently reappearing again.

• Documentation

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    • README

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[codecov-commenter]

Codecov Report

Attention: 24 lines in your changes are missing coverage. Please review.

Comparison is base (f1b9436) 82.64% compared to head (cdc83fb) 81.06%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
cache.go	52.17%	19 Missing and 3 partials ⚠️
internal/queue/mpsc.go	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
- Coverage   82.64%   81.06%   -1.59%     
==========================================
  Files           9        9              
  Lines         657      713      +56     
==========================================
+ Hits          543      578      +35     
- Misses         99      119      +20     
- Partials       15       16       +1     

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