[quantization] Add as_raw_ptr.

[hildebrandmw]

Add publicly exported as_raw_ptr for retrieving the base pointer of Mat, MatRef, and MatMut.

The term "raw" is meant to denote that this is the byte pointer - not necessarily the pointer to the actual element type stored in these containers.

[Copilot]

Pull request overview

This pull request adds a new public method as_raw_ptr() to the Mat, MatRef, and MatMut types in the quantization module. The method provides safe access to the underlying byte-level pointer (*const u8) for these matrix types. The "raw" naming convention clearly distinguishes this byte-pointer accessor from potential typed-pointer accessors, following established codebase patterns.

Changes:

• Added as_raw_ptr() method to Mat, MatRef, and MatMut that returns the base byte pointer (*const u8)
• Removed the previous test-only as_ptr() method from Mat and replaced all its usages with the new public as_raw_ptr()
• Updated all test code to use the new method name

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.99%. Comparing base (e093583) to head (a84331d).

Files with missing lines	Patch %	Lines
diskann-quantization/src/multi_vector/matrix.rs	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #774      +/-   ##
==========================================
- Coverage   88.99%   88.99%   -0.01%     
==========================================
  Files         428      428              
  Lines       78415    78431      +16     
==========================================
+ Hits        69784    69798      +14     
- Misses       8631     8633       +2     

Flag	Coverage Δ
miri	88.99% <91.30%> (-0.01%)	⬇️
unittests	88.99% <91.30%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
diskann-quantization/src/multi_vector/matrix.rs	97.28% <91.30%> (-0.25%)	⬇️

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[arkrishn94]

I'm curious - why expose these publicly?

[arkrishn94]

Isn't this a footgun for unsafe reads?