enhance: [2.5] Reduce mutex contention in datacoord meta

[bigsheeper]

1. Using secondary index to avoid retrieving all segments at GetSegmentsChanPart.
2. Perform batch SetAllocations to reduce the number of times the meta lock is acquired.

issue: #37630

pr: #38219

[sre-ci-robot]

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[mergify]

@bigsheeper go-sdk check failed, comment rerun go-sdk can trigger the job again.

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 6 lines in your changes missing coverage. Please review.

Project coverage is 81.06%. Comparing base (6fa096e) to head (a900127).

Files with missing lines	Patch %	Lines
internal/datacoord/meta.go	40.00%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              2.5   #38904   +/-   ##
=======================================
  Coverage   81.05%   81.06%           
=======================================
  Files        1383     1383           
  Lines      195503   195513   +10     
=======================================
+ Hits       158472   158499   +27     
+ Misses      31457    31454    -3     
+ Partials     5574     5560   -14     

Components	Coverage Δ
Client	78.26% <ø> (ø)
Core	69.45% <ø> (-0.02%)	⬇️
Go	83.05% <78.57%> (+0.01%)	⬆️

Files with missing lines	Coverage Δ
internal/datacoord/compaction_policy_clustering.go	75.48% <100.00%> (-0.12%)	⬇️
internal/datacoord/compaction_policy_single.go	61.00% <100.00%> (-0.39%)	⬇️
internal/datacoord/compaction_trigger.go	85.53% <100.00%> (+0.39%)	⬆️
internal/datacoord/segment_info.go	84.72% <100.00%> (ø)
internal/datacoord/meta.go	89.32% <40.00%> (-0.37%)	⬇️

... and 31 files with indirect coverage changes