opt: speed up ReleaseTimeout() for multi-pool

[panjf2000]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 12 lines in your changes missing coverage. Please review.

Project coverage is 90.88%. Comparing base (95dad45) to head (05edbd0).

Files	Patch %	Lines
multipool.go	72.72%	4 Missing and 2 partials ⚠️
multipool_func.go	72.72%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #332      +/-   ##
==========================================
- Coverage   91.04%   90.88%   -0.16%     
==========================================
  Files          11       11              
  Lines         804      834      +30     
==========================================
+ Hits          732      758      +26     
- Misses         50       51       +1     
- Partials       22       25       +3     

Flag	Coverage Δ
unittests	90.88% <72.72%> (-0.16%)	⬇️

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