test(s3vectors): add an opt-in end-to-end perf suite for vector buckets (#12297)

* test(s3vectors): add an opt-in end-to-end perf suite

perf_test.py runs on the same cluster fixture as the integration suite
(Go or Rust volume, single or distributed queries) and times the data
plane through the S3 Vectors API: PutVectors ingest and upsert, QueryVectors
latency with and without metadata and a 10% filter, query throughput
across client threads, GetVectors, segmented ListVectors, and
DeleteVectors. Recall is checked against an exact client-side search and
listings must be complete; timings only report. Sizes come from PERF_*
variables, and results go to a JSON report and a printed summary.

It runs through run_perf.sh or `make perf`. run_test.sh does not collect
it, so CI is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): check every listed key in the perf suite, not just the count

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): cap perf samples at PERF_VECTORS so small runs work

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): warm perf worker clients before starting throughput timers

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

* test(s3vectors): report the key count of perf GetVectors and DeleteVectors calls

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011UpvafvK8JpagF94MHWqwK

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/s3vectors/run_perf.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")"
+exec "${PYTHON:-python3}" -m pytest -xvs perf_test.py "$@"