Strengthen arguments to robust_prune.

[Mark Hildebrand (hildebrandmw)]

Make the sorted_cache argument a SortedNeighbors instead to structurally require sortedness. This removes the Eq bound from SortedNeighbors, which is left over from #1273, and provides a helper map_in for projecting SortedNeighbors.

[Copilot]

Pull request overview

This PR strengthens the graph::internal::prune::robust_prune API by requiring its candidate input to be a SortedNeighbors, making the sorted-by-distance invariant structural rather than a debug assertion. It also removes the lingering Eq bound from SortedNeighbors (left over from #1273) and introduces a SortedNeighbors::map_in helper to project a sorted neighbor list into another storage buffer while preserving sortedness.

Changes:

• Change robust_prune to accept SortedNeighbors<'_, Option<V>> instead of a raw &[(f32, Option<V>)], removing the runtime sortedness assertion.
• Refactor SortedNeighbors to drop the Eq bound and add map_in to project IDs into a separate, linearly accessible cache while preserving order.
• Extend VerboseEq support in tests (notably for str and references).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
diskann/src/test/cmp.rs	Adds VerboseEq impl for references and expands leaf VerboseEq coverage (incl. str).
diskann/src/graph/internal/sorted_neighbors.rs	Drops Eq constraint, makes SortedNeighbors Copy/Clone, adds map_in, and adds tests for mapping behavior.
diskann/src/graph/internal/prune.rs	Updates robust_prune to accept SortedNeighbors candidates and adapts indexing/lookup logic accordingly.
diskann/src/graph/index.rs	Uses SortedNeighbors::map_in to build the prune candidate cache and updates the robust_prune call site.

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[Codecov Comments Bot (codecov-commenter)]

Codecov Report

❌ Patch coverage is 93.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.55%. Comparing base (158126e) to head (cb09c2d).

Files with missing lines	Patch %	Lines
diskann/src/graph/internal/sorted_neighbors.rs	93.02%	3 Missing ⚠️
diskann/src/graph/internal/prune.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1358      +/-   ##
==========================================
- Coverage   91.55%   91.55%   -0.01%     
==========================================
  Files         521      521              
  Lines      100371   100410      +39     
==========================================
+ Hits        91898    91927      +29     
- Misses       8473     8483      +10     

Flag	Coverage Δ
miri	91.55% <93.33%> (-0.01%)	⬇️
unittests	91.23% <93.33%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
diskann/src/graph/index.rs	96.47% <100.00%> (-0.02%)	⬇️
diskann/src/test/cmp.rs	98.37% <100.00%> (+0.02%)	⬆️
diskann/src/graph/internal/prune.rs	84.90% <85.71%> (-0.15%)	⬇️
diskann/src/graph/internal/sorted_neighbors.rs	96.47% <93.02%> (-3.53%)	⬇️

... and 4 files with indirect coverage changes

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