fix:use refcount to avoid remove connection using by multi-clients

[jac0626]

use refcount to avoid remove connection using by multi-clients
also see #3132

[sre-ci-robot]

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[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@7ac0d68). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pymilvus/milvus_client/_utils.py	50.00%	1 Missing ⚠️
pymilvus/milvus_client/async_milvus_client.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3140   +/-   ##
=========================================
  Coverage          ?   46.51%           
=========================================
  Files             ?       66           
  Lines             ?    14012           
  Branches          ?        0           
=========================================
  Hits              ?     6518           
  Misses            ?     7494           
  Partials          ?        0           

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