fix: review #144 copilot and fix bugs…

[vcaesar]

• Update hnsw.go and 5 others

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Description

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[Copilot]

🟢 Approval recommended

No unresolved blocking issues were identified, and the changes include comprehensive regression coverage.

Pull request overview

Adds cancellation-aware approximate vector search, improved filtered HNSW traversal, and parameter validation.

Changes:

• Propagates cancellation through ANN search and cache construction.
• Supports rejected-node bridge traversal and filter fast paths.
• Adds regression tests for cancellation, filtering, and overflow.

File summaries

File	Summary
search/knn/knn_test.go	Tests approximate-search cancellation propagation.
index/snapshot_vector.go	Propagates contexts and optimizes filters.
index/snapshot_vector_test.go	Updates nil-filter test support.
index/segment_vector_test.go	Tests cache cancellation and filter fast paths.
hnsw/hnsw.go	Adds context-aware search and parameter validation.
hnsw/hnsw_test.go	Tests cancellation, filtering, bridges, and overflow.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0
• Review effort level: Lite

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