feat: add vector quantization configuration

[zhangzhenghao]

Summary

This PR adds vector quantization and HNSW index configuration support for vector databases.

Changes

1. VectorConfig struct - Unified configuration for quantization and HNSW parameters
2. Database interface - Updated AddCollection to accept VectorConfig
3. Quantization support per database:
   • Milvus: SQ (int8), PQ
   • Qdrant: SQ (int8), PQ
   • Weaviate: PQ only
   • SQLite: Not supported (returns error)

Quantization Types

Type	Memory Saving	Description
none	0%	float32 vectors (default)
sq	75%	Scalar quantization (int8)
pq	~90%	Product quantization

Configuration Example

[database.vector]
quantization = "sq"  # none | sq | pq
sq_bits = 8          # SQ bits (only 8 supported)
pq_subvectors = 8    # PQ subvector count
pq_bits = 8          # PQ bits per subvector
hnsw_m = 16          # HNSW M parameter
hnsw_ef_construction = 200
hnsw_ef_search = 64

Breaking Change

The AddCollection method signature has changed.

TODO

• Regenerate protobuf files
• Add tests for quantization configurations

[codecov]

Codecov Report

❌ Patch coverage is 69.77226% with 146 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.49%. Comparing base (83a2266) to head (4f581c7).

Files with missing lines	Patch %	Lines
storage/vectors/milvus.go	67.39%	28 Missing and 17 partials ⚠️
storage/vectors/qdrant.go	76.85%	24 Missing and 4 partials ⚠️
storage/vectors/weaviate.go	72.85%	14 Missing and 5 partials ⚠️
master/master.go	59.52%	9 Missing and 8 partials ⚠️
storage/vectors/sqlite.go	57.50%	12 Missing and 5 partials ⚠️
storage/vectors/database.go	0.00%	12 Missing ⚠️
storage/vectors/proxy.go	84.61%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1261      +/-   ##
==========================================
- Coverage   73.67%   73.49%   -0.18%     
==========================================
  Files          93       93              
  Lines       17316    17739     +423     
==========================================
+ Hits        12757    13037     +280     
- Misses       3214     3312      +98     
- Partials     1345     1390      +45     

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