[diskann-garnet] Fix cache coherence on set_neighbors

[metajack]

When diagnosing some issues last week I realized that there was a cache coherency problem with set_neighbors(). append_vector() updates the start point neighbor cache atomically alongside the real neighbor list, but set_neighbors() did two writes sequentially which could result in coherency issues.

As far as I'm aware, this did not cause any actual problems, but it was easy enough to make it coherent by using RMW instead in set_neighbors().

[Copilot]

Pull request overview

This PR addresses a cache-coherency window in diskann-garnet where set_neighbors() updated Garnet storage and the start-point neighbor cache via two separate operations. It aligns set_neighbors() with the existing append_vector() pattern by performing the update via a read-modify-write (RMW) callback, and bumps the crate/package version to reflect the fix.

Changes:

• Update GarnetProvider::set_neighbors() to use Callbacks::rmw_iid() and update the start-point neighbor cache within the same RMW operation.
• Standardize error returns to GarnetError::Write.into() for write failures in the modified code paths.
• Bump diskann-garnet version from 3.0.0 to 3.0.1 across Rust and NuGet packaging metadata.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
diskann-garnet/src/provider.rs	Switch set_neighbors() to an RMW update to avoid cache/storage coherence windows; minor error return normalization.
diskann-garnet/diskann-garnet.nuspec	Bump NuGet package version to 3.0.1.
diskann-garnet/Cargo.toml	Bump crate version to 3.0.1.
Cargo.lock	Update lockfile entry for diskann-garnet to 3.0.1.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.71%. Comparing base (9123eb5) to head (afe5890).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
diskann-garnet/src/provider.rs	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1230      +/-   ##
==========================================
+ Coverage   89.64%   89.71%   +0.07%     
==========================================
  Files         503      503              
  Lines       95761    96009     +248     
==========================================
+ Hits        85845    86139     +294     
+ Misses       9916     9870      -46     

Flag	Coverage Δ
miri	89.71% <83.33%> (+0.07%)	⬆️
unittests	89.38% <83.33%> (+0.07%)	⬆️

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

Files with missing lines	Coverage Δ
diskann-garnet/src/provider.rs	74.80% <83.33%> (+0.09%)	⬆️

... and 10 files with indirect coverage changes

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[harsha-simhadri]

Could you share before and after perf numbers? Perhaps we should make it easier to run some of these going forward