next.js

80730456 - Add perf marks, benchmark runner, and restore OTel startResponse span

Add perf marks, benchmark runner, and restore OTel startResponse span - Add opt-in perf marks module (NEXT_PERF_MARKS=1) for SSR phase timing - Add benchmark runner (bench/basic-app/run-bench.js) with CPU profiling and auto-comparison - Restore NextNodeServer.startResponse to NextVanillaSpanAllowlist (fixes OTel test) - Update AGENTS.md with benchmarking docs and streaming pipeline notes - Enhance minimal-server with perf marks collection and CPU profiling support