feat: add SQ4U scalar quantization type for Milvus HNSW index

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Ubuntu

vectordb_bench/backend/clients/api.py

@@ -49,6 +49,7 @@ class IndexType(StrEnum):
 
 
 class SQType(StrEnum):
+    SQ4U = "SQ4U"
     SQ6 = "SQ6"
     SQ8 = "SQ8"
     BF16 = "BF16"

vectordb_bench/backend/clients/milvus/cli.py

@@ -242,8 +242,8 @@ class MilvusHNSWSQTypedDict(CommonTypedDict, MilvusTypedDict, MilvusHNSWTypedDic
         str | None,
         click.option(
             "--sq-type",
-            type=click.Choice(["SQ6", "SQ8", "BF16", "FP16", "FP32"], case_sensitive=False),
-            help="Scalar quantizer type. Supported values: SQ6,SQ8,BF16,FP16,FP32",
+            type=click.Choice(["SQ4U", "SQ6", "SQ8", "BF16", "FP16", "FP32"], case_sensitive=False),
+            help="Scalar quantizer type. Supported values: SQ4U,SQ6,SQ8,BF16,FP16,FP32",
             required=True,
         ),
     ]