[Backport 2.5] add more pooling method and refactor

[opensearch-trigger-bot]

Backport d7f3c86 from #672

[codecov-commenter]

Codecov Report

Merging #679 (72cc2b0) into 2.5 (2fca056) will decrease coverage by 0.81%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.5     #679      +/-   ##
============================================
- Coverage     84.18%   83.36%   -0.82%     
+ Complexity     1010      994      -16     
============================================
  Files            93       93              
  Lines          3660     3660              
  Branches        342      342              
============================================
- Hits           3081     3051      -30     
- Misses          435      463      +28     
- Partials        144      146       +2     

Flag	Coverage Δ
ml-commons	83.36% <ø> (-0.82%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ain/java/org/opensearch/ml/model/MLModelCache.java	86.36% <ø> (ø)
.../cluster/MLCommonsClusterManagerEventListener.java	65.62% <0.00%> (-12.50%)	⬇️
...org/opensearch/ml/cluster/DiscoveryNodeHelper.java	89.39% <0.00%> (-9.10%)	⬇️
...ain/java/org/opensearch/ml/task/MLTaskManager.java	59.39% <0.00%> (-6.60%)	⬇️
...n/java/org/opensearch/ml/cluster/MLSyncUpCron.java	87.50% <0.00%> (-6.25%)	⬇️
.../ml/action/syncup/TransportSyncUpOnNodeAction.java	85.71% <0.00%> (-4.09%)	⬇️

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