Added test for K means

[arrayka]

• Does this PR have a descriptive title that could go in our release notes?
• Does this PR add any new dependencies?
• Does this PR modify any existing APIs?
• Is the change to the API backwards compatible?
• Should this result in any changes to our documentation, either updating existing docs or adding new ones?

Reference Issues/PRs

What does this implement/fix? Briefly explain your changes.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.51%. Comparing base (205aad7) to head (17844b9).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1095      +/-   ##
==========================================
+ Coverage   89.46%   89.51%   +0.04%     
==========================================
  Files         459      458       -1     
  Lines       85482    85583     +101     
==========================================
+ Hits        76475    76608     +133     
+ Misses       9007     8975      -32     

Flag	Coverage Δ
miri	89.51% <100.00%> (+0.04%)	⬆️
unittests	89.13% <100.00%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
diskann-disk/src/utils/kmeans.rs	96.62% <100.00%> (+5.64%)	⬆️

... and 24 files with indirect coverage changes

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