enhance: [2.4] 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]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 6 lines in your changes missing coverage. Please review.

Project coverage is 79.45%. Comparing base (6f573f6) to head (7ee272c).
Report is 2 commits behind head on 2.4.

Files with missing lines	Patch %	Lines
internal/datacoord/meta.go	33.33%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.4   #38230      +/-   ##
==========================================
+ Coverage   72.15%   79.45%   +7.30%     
==========================================
  Files        1077     1077              
  Lines      169342   169347       +5     
==========================================
+ Hits       122185   134555   +12370     
+ Misses      42685    30313   -12372     
- Partials     4472     4479       +7     

Files with missing lines	Coverage Δ
internal/datacoord/compaction_policy_clustering.go	75.24% <100.00%> (-0.12%)	⬇️
internal/datacoord/compaction_policy_single.go	60.60% <100.00%> (-0.40%)	⬇️
internal/datacoord/compaction_trigger.go	84.04% <100.00%> (-1.06%)	⬇️
internal/datacoord/meta.go	87.83% <33.33%> (-0.41%)	⬇️

... and 252 files with indirect coverage changes

[bigsheeper]

rerun ut