Fix argmin/argmax based on the distance type

[achirkin]

Fix the distance type not taken into account when generating ground truth on GPU.

[tfeher]

LGTM.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 5f7d5a6 and 102a03a.

📒 Files selected for processing (1)

• python/cuvs_bench/cuvs_bench/generate_groundtruth/__main__.py

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Corrected the ranking order for the inner_product metric when selecting top-k neighbors in groundtruth generation, ensuring accurate benchmark results.

Walkthrough

The change updates the top-k neighbor selection logic in the calc_truth function to correctly handle the "inner_product" metric. When merging results from batched distance computations, the code now negates distances for "inner_product" before sorting, ensuring the highest inner products are selected as top-k neighbors rather than the lowest.

Changes

Inner Product Metric Handling in Top-K Selection

Layer / File(s)	Summary
Top-K Selection with Metric-Aware Sort Keys python/cuvs_bench/cuvs_bench/generate_groundtruth/__main__.py	Top-k neighbor selection after batch concatenation now computes sort keys that negate distances when metric == "inner_product", ensuring correct ordering before argsort and final index reordering.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly addresses the main change: fixing argmin/argmax logic based on distance type, which aligns with the code modification that handles inner_product metric differently.
Description check	✅ Passed	The description is directly related to the changeset, explaining that the fix addresses the distance type not being taken into account when generating ground truth on GPU.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-calc-truth-for-inner-product-1

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