Fix IDSelector handling in unbounded HNSW search

[YingzuoLiu]

Summary

• apply SearchParametersHNSW.sel to the unbounded HNSW search path
• keep filtered nodes available for graph traversal while excluding them from the result set
• add regression coverage for L2 and inner-product search, restrictive efSearch, and an empty selector

Root cause

The bounded HNSW path applies the selector through its result handler. The unbounded path did not receive the selector and used the same heap for traversal pruning and final results, so IDs rejected by SearchParameters.sel could be returned.

Implementation

When a selector is present, the unbounded path maintains a separate result heap containing only accepted IDs. The existing candidate heap remains unchanged and can still contain rejected nodes, preserving traversal through them. The selector-free path keeps its existing compile-time specialization and behavior.

Validation

• issue reproducer: unbounded search now returns ID 1 at distance 100.0 instead of rejected ID 0
• tests/test_search_params.py: 51 passed
• HNSW C++ tests: 7 passed
• full CPU C++ test suite: 273 passed, 5 skipped, 0 failed
• clang-format and git diff --check: passed

Fixes #5504

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