feat: return scores from vector queries

[zhangzhenghao]

Summary

• add ScoredVector and make QueryVectors return vector similarity scores
• propagate scores from SQLite, Qdrant, Milvus, and Weaviate with higher values meaning greater similarity
• carry scored vectors through the vector-store gRPC proxy by changing QueryVectorsResponse.vectors field 1 directly to ScoredVector
• add a shared dot-product test that verifies query results are ordered by descending score

Score semantics

• Qdrant: use the native query score
• Milvus: use the native score and negate L2 distance
• SQLite and Weaviate: negate distance

Testing

• go test ./storage/vectors -run '^(TestNoDatabase|TestSQLite|TestProxy)$' -count=1
• go vet ./storage/vectors ./protocol
• go test ./protocol ./storage/vectors ./logics ./master ./server ./worker -run '^$'
• go test ./... -run '^$' -count=1
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 58.97436% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.64%. Comparing base (ea88b44) to head (d4522a9).

Files with missing lines	Patch %	Lines
storage/vectors/milvus.go	0.00%	28 Missing ⚠️
storage/vectors/sqlite.go	75.00%	1 Missing and 1 partial ⚠️
storage/vectors/qdrant.go	90.00%	1 Missing ⚠️
storage/vectors/weaviate.go	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1355      +/-   ##
==========================================
+ Coverage   72.28%   72.64%   +0.36%     
==========================================
  Files          94       94              
  Lines       18278    18312      +34     
==========================================
+ Hits        13212    13303      +91     
+ Misses       3660     3634      -26     
+ Partials     1406     1375      -31     

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