Remove direct accessor call in diskann-garnet

[hildebrandmw]

In preparation for #1067, switch the implementation of DynIndex::search_element from using the Accessor trait to an inherent method on the underlying provider.

[Copilot]

Pull request overview

This PR updates diskann-garnet to avoid using the Accessor trait (and a per-call Tokio runtime) when implementing DynIndex::search_element, in preparation for the trait simplification work described in #1067. Instead, it centralizes the “read one vector by internal id” logic as an inherent method on GarnetProvider.

Changes:

• Added GarnetProvider::get_vector(...) as a crate-visible helper for reading a single vector (including the start-point fast path).
• Switched DynIndex::search_element to use provider.get_vector(...) directly, removing the Tokio runtime + Accessor usage.
• Refactored FullAccessor::get_element to delegate to GarnetProvider::get_vector(...) to avoid duplicated logic.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
diskann-garnet/src/provider.rs	Introduces get_vector and reuses it in the Accessor implementation.
diskann-garnet/src/dyn_index.rs	Removes the Accessor/Tokio runtime path and calls GarnetProvider::get_vector directly.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.36364% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.49%. Comparing base (c667a3c) to head (b4b197a).

Files with missing lines	Patch %	Lines
diskann-garnet/src/provider.rs	90.47%	2 Missing ⚠️
diskann-garnet/src/dyn_index.rs	0.00%	1 Missing ⚠️

❌ Your patch status has failed because the patch coverage (86.36%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1098      +/-   ##
==========================================
+ Coverage   89.48%   89.49%   +0.01%     
==========================================
  Files         474      474              
  Lines       89740    89737       -3     
==========================================
+ Hits        80301    80312      +11     
+ Misses       9439     9425      -14     

Flag	Coverage Δ
miri	89.49% <86.36%> (+0.01%)	⬆️
unittests	89.14% <86.36%> (+0.01%)	⬆️

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

Files with missing lines	Coverage Δ
diskann-garnet/src/dyn_index.rs	74.19% <0.00%> (+9.40%)	⬆️
diskann-garnet/src/provider.rs	83.55% <90.47%> (+0.18%)	⬆️

... and 2 files with indirect coverage changes

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