Add attribute rendering benchmark (#95621)
### What?
Add two dynamic routes to the render-pipeline benchmark and include both
in the default route suite:
- `/attributes` renders 1,000 rows with string, data, ARIA, title, and
inline-style attributes.
- `/tailwind` renders a realistic dashboard with dense Tailwind-style
utility class names across navigation, metrics, project cards, and an
activity table.
### Why?
The existing benchmark routes focus on lightweight rendering or Suspense
and Flight payload stress. They do not provide focused integration
coverage for React Fizz attribute serialization.
`/attributes` provides a synthetic stress case modeled after the
upstream React benchmark for facebook/react#36899. `/tailwind`
complements it with a production-like component tree and realistic class
strings, including responsive, state, dark-mode, and arbitrary-value
utilities.
### How?
Both fixtures run through the real Next.js production-server
render-pipeline harness and are forced dynamic so every request
exercises server rendering.
The Tailwind-style fixture contains 18 project cards, 36 activity rows,
and 101 `className` attributes. It intentionally does not install or
configure Tailwind because the benchmark targets React serialization of
the class strings, not generated CSS or visual styling.
The new routes are registered in the default stress suite and documented
in the benchmark playbook and render-pipeline README.
### Verification
- Prettier for all changed files
- ESLint for both benchmark fixtures and
`bench/render-pipeline/benchmark.ts`
- Production `next build` + `next start` smoke benchmark for
`/tailwind`; single-client and under-load phases completed with zero
request errors
- Three interleaved base/head `/attributes` runs with 500 serial and
5,000 loaded requests
- `/attributes` PR-head median throughput: +8.26% single-client and
+10.85% under load
- `/attributes` PR-head median p95: 7.91% better single-client and 9.61%
better under load
- `git diff --check`
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