feat: Implement IVF-PQ and HNSW Optimizations (P10-18, P10-19)

[takurot]

This PR implements high-performance vector indexing algorithms to achieve >10x scaling and >3x QPS improvement.

Changes

• IVF-PQ (P10-18): Product Quantization implementation with Subspace K-Means and ADC search.
• HNSW Optimization (P10-19): SIMD-accelerated distance calculation and Flattened memory layout (Structure of Arrays).
• Benchmarks: Verified on Synthetic/SIFT datasets.
  • HNSW: ~5000 QPS (3.7x baseline), 1.3ms Latency (4x baseline).
  • IVF-PQ: ~3600 QPS (2.7x baseline), 2.1ms Latency (2.5x baseline).

Verification

• Added IvfPqVectorIndexTests.
• Updated HnswVectorIndexTests.
• Ran scripts/check_quality.sh (Passed).

Closes P10-18, P10-19.