fix: slight cleanups to path handling so that the indices builder tool properly supports Windows

[westonpace]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.59%. Comparing base (712405e) to head (5f269ff).
Report is 1 commits behind head on main.

Files	Patch %	Lines
rust/lance-index/src/vector/ivf/shuffler.rs	0.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2689      +/-   ##
==========================================
- Coverage   79.61%   79.59%   -0.02%     
==========================================
  Files         226      226              
  Lines       66516    66523       +7     
  Branches    66516    66523       +7     
==========================================
- Hits        52955    52948       -7     
- Misses      10465    10471       +6     
- Partials     3096     3104       +8     

Flag	Coverage Δ
unittests	79.59% <0.00%> (-0.02%)	⬇️

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