feat: add support for Alibaba Cloud AnalyticDB for PostgreSQL Nova

[softhuafei]

Summary

Adds a new client adbpgnova for Alibaba Cloud AnalyticDB for PostgreSQL (ADB-PG), which supports the Nova vector index
family (novamr / novad) backed by the fastann engine and USING ann syntax.

What's added

• Client implementation: vectordb_bench/backend/clients/adbpg/{adbpg.py,config.py,cli.py}
• CLI command: vectordbbench adbpgnova ...
• Frontend integration: db case configs + style entry, so the new client shows up in the Streamlit UI
• Unit tests: tests/test_adbpg.py — 9 tests covering config defaults, to_dict connection options, index_param WITH-clause options (incl. raw auto_reduction=on), session_param
  GUC emission, and TestResult.read_file round-trip
• README: a new "Run ADBPG (Aliyun AnalyticDB for PostgreSQL) from command line" section with examples

Algorithms supported

Algorithm	Build params	Search GUCs
novamr (default)	hnsw_m, ef_construction, rabitq_bits, auto_reduction	fastann.hnsw_ef_search, fastann.hnsw_max_scan_points, fastann.quantize_rescore_amp, fastann.nova_adaptive_gamma
novad	nlist, rabitq_bits	fastann.nova_nprobe (exposed as --nprobe)

Example

vectordbbench adbpgnova --case-type Performance768D1M --k 10 \
  --host <host> --port 5432 --db-name postgres \
  --user-name <user> --password <pwd> \
  --algorithm novamr --hnsw-m 48 --ef-construction 600 \
  --ef-search 50 --max-scan-points 16000 --quantize-rescore-amp 0.6 \
  --auto-reduction --num-concurrency 48

Or via YAML:

vectordbbench adbpgnova --config-file adbpg_cohere1m_novamr.yml

Test plan

• make lint (black + ruff) passes locally
• pytest tests/test_adbpg.py — 9/9 passing
• End-to-end runs against a live ADB-PG cluster for both algorithms (no-filter and 1%-filter cases)
• Streamlit Results page renders the saved JSON correctly

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[softhuafei]

/assign @XuanYang-cn