[release-21.0] Use proper zstd decoder pool for binlog event compression handling (#17042)

[vitess-bot]

Description

This is a backport of #17042

[vitess-bot]

Review Checklist

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General

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[codecov]

Codecov Report

Attention: Patch coverage is 73.52941% with 9 lines in your changes missing coverage. Please review.

Project coverage is 67.24%. Comparing base (736e54d) to head (e957e2f).
Report is 1 commits behind head on release-21.0.

Files with missing lines	Patch %	Lines
go/mysql/binlog_event_compression.go	73.52%	9 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-21.0   #17045      +/-   ##
================================================
+ Coverage         67.23%   67.24%   +0.01%     
================================================
  Files              1570     1570              
  Lines            251256   251264       +8     
================================================
+ Hits             168937   168971      +34     
+ Misses            82319    82293      -26     

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