enhance: optimize the loading index performance (#29894)

[yah01]

this utilizes concurrent loading
pr: #29894

[mergify]

@yah01 E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (81fdb6f) 82.20% compared to head (60efe08) 82.21%.
Report is 21 commits behind head on 2.3.

Additional details and impacted files

@@           Coverage Diff           @@
##              2.3   #30018   +/-   ##
=======================================
  Coverage   82.20%   82.21%           
=======================================
  Files         834      825    -9     
  Lines      120405   120349   -56     
=======================================
- Hits        98984    98940   -44     
+ Misses      18193    18182   -11     
+ Partials     3228     3227    -1     

Files	Coverage Δ
internal/core/src/index/VectorMemIndex.cpp	65.81% <0.00%> (+2.18%)	⬆️

... and 160 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

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