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

[mergify]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.06%. Comparing base (5199415) to head (1f8e984).
Report is 3 commits behind head on 2.5.

Additional details and impacted files

@@             Coverage Diff             @@
##              2.5   #38904       +/-   ##
===========================================
+ Coverage   69.58%   81.06%   +11.47%     
===========================================
  Files         297     1399     +1102     
  Lines       26557   196789   +170232     
===========================================
+ Hits        18480   159521   +141041     
- Misses       8077    31657    +23580     
- Partials        0     5611     +5611     

Components	Coverage Δ
Client	78.26% <ø> (∅)
Core	69.58% <ø> (ø)
Go	83.02% <100.00%> (∅)

Files with missing lines	Coverage Δ
internal/datacoord/compaction_policy_clustering.go	75.48% <100.00%> (ø)
internal/datacoord/compaction_policy_single.go	61.00% <100.00%> (ø)
internal/datacoord/compaction_trigger.go	85.53% <100.00%> (ø)
internal/datacoord/meta.go	89.66% <100.00%> (ø)
internal/datacoord/segment_info.go	84.72% <100.00%> (ø)

... and 1097 files with indirect coverage changes

[mergify]

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[xiaofan-luan]

/lgtm
/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bigsheeper, xiaofan-luan

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