chore: reuse the scheduler during reading shuffled partitions

[BubbleCal]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.65%. Comparing base (0dbfc7c) to head (35be399).

Files	Patch %	Lines
rust/lance/src/index/vector/builder.rs	50.00%	0 Missing and 2 partials ⚠️
rust/lance-index/src/vector/v3/shuffler.rs	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2528      +/-   ##
==========================================
- Coverage   79.66%   79.65%   -0.02%     
==========================================
  Files         207      207              
  Lines       59179    59174       -5     
  Branches    59179    59174       -5     
==========================================
- Hits        47147    47136      -11     
- Misses       9256     9258       +2     
- Partials     2776     2780       +4     

Flag	Coverage Δ
unittests	79.65% <70.00%> (-0.02%)	⬇️

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