feat: add VolcanoMilvus DISKANN support

[lyxiong0]

Summary

Add VolcanoMilvus as a new VectorDBBench target by extending the existing Milvus client with Volcano-specific DISKANN behavior.

What's added

• New VolcanoMilvus client implementation under vectordb_bench/backend/clients/volcano_milvus/

• New CLI command: vectordbbench volcanomilvusdiskann ...

• Volcano DISKANN config support:

  • build params: max_degree, build_search_list, legacy, store_strategy, quant_type, num_threads, distance_strategy

• Load behavior knobs: load_reqs_size and load_after_compaction

• Frontend integration for Load, Performance, and Streaming benchmark cases

• README/model enum updates so VolcanoMilvus is discoverable as a supported client

• Unit tests for CLI parsing, frontend config exposure, load/search params, and DISKANN-only case mapping

Supported index

Only DISKANN is exposed for VolcanoMilvus in this change. Other index types do not fall back to the upstream Milvus configs silently.

Example

vectordbbench volcanomilvusdiskann \
  --case-type Performance768D10M \
  --k 10 \
  --num-concurrency 400 \
  --uri <uri> \
  --user-name <user-name> \
  --password <pass> \
  --search-list 300 \
  --max-degree 48  \
  --replica-number 1 \
  --num-shards 1 \
  --load-after-compaction  \
  --distance-strategy "quant then full" \
  --num-threads 64 \
  --concurrency-duration 30 \
  --enable-thp 
  --enable-prefetch

[sre-ci-robot]

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