Add http/https vs fetch transport benchmark for the Node.js client

[Copilot]

Summary

The issue proposes replacing the Node.js client's legacy http/https transport with fetch/undici for performance, and the discussion asks for trustworthy comparison data before committing to a rewrite. This PR adds a reproducible benchmark that pits the current client against a trivial fetch() (undici) stub over identical requests — no transport rewrite yet, just the data to justify one.

• benchmarks/transport/ — new benchmark:
  • clients.ts — a TransportClient abstraction with two impls driven through the same scenarios: SdkTransportClient (@clickhouse/client, uses exec() to isolate transport from row parsing) and FetchTransportClient (minimal fetch() stub).
  • index.ts — runner for three use cases with warmup + configurable iterations and p50/p90/p99 latency: single-request latency (SELECT 1), download throughput (large result set), upload throughput (POST to null() so no table setup is needed). Tunable via CLICKHOUSE_URL, LATENCY_REQUESTS, DOWNLOAD_ROWS, UPLOAD_ROWS, ITERATIONS, WARMUP.
  • stats.ts — dependency-free latency/throughput helpers.
  • README.md — run instructions, config, interpretation, sample local run.
• Tooling fixes to make benchmarks buildable/lintable:
  • benchmarks/tsconfig.json extended a non-existent ../tsconfig.json → now ../tsconfig.base.json; registers transport/**/*.ts.
  • Added benchmarks/eslint.config.mjs so benchmark files have a discoverable flat config (ESLint v10 + lint-staged otherwise error on staged benchmark files).

Indicative single local run (sandbox, Node 24, loopback):

Scenario	@clickhouse/client (http/https)	fetch (undici) stub
SELECT 1 latency (mean)	2.49 ms	1.74 ms
Download throughput	273 MiB/s	68 MiB/s
Upload throughput	40 MiB/s	40 MiB/s

Early signal is a trade-off rather than a clear win: fetch has lower small-request latency, the existing streaming path drains large downloads faster, and uploads are server-bound for both. Numbers are environment-specific and meant to be re-run per workload.

docker-compose up -d
tsc --project benchmarks/tsconfig.json \
  && node benchmarks/dist/benchmarks/transport/index.js

Checklist

• A human-readable description of the changes was provided to include in CHANGELOG

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