refactor(test): move slow vector index tests to integration tests

[wjones127]

Summary

• Move compute-heavy vector index tests from unit test modules to integration tests
• Tests run with opt-level=1 in the query-integration-tests CI job for better performance
• Prevents CI timeouts caused by debug build slowness (6.5x slower than optimized)

Tests migrated:

• test_build_ivf_pq, test_build_ivf_pq_v3, test_build_ivf_pq_4bit
• test_create_ivf_hnsw_pq, test_create_ivf_hnsw_pq_4bit
• test_optimize_with_empty_partition, test_remap_join_on_second_delta
• test_create_index_with_many_invalid_vectors
• test_build_pq_model_l2, test_build_pq_model_cosine

Test plan

• cargo check -p lance --features slow_tests --tests passes
• cargo clippy -p lance --features slow_tests --tests passes
• CI passes

🤖 Generated with Claude Code

[github-actions]

PR Review Summary

This is a well-organized refactoring that moves compute-heavy vector index tests to integration tests. The change is straightforward and the motivation (CI timeout prevention) is sound.

Minor Observations

P1: Possible test coverage gap in moved tests

The original tests in v2.rs called multiple test helpers like test_remap, test_distance_range, test_index_multivec, and test_delete_all_rows in addition to the basic index creation. The new integration tests (ivf_pq.rs, ivf_hnsw.rs) only call test_recall. While some of these may be covered elsewhere, it's worth verifying that remap/delete functionality remains tested for these index types.

Note: test_spfresh_join_split was correctly kept in unit tests since it requires private API access - good decision documented in the PR.

Overall

The migration is clean, the shared utilities in utils.rs are well-factored, and the feature flag gating via slow_tests is appropriate. No bugs or security concerns identified.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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