bench/results records a cold forge at 500/s on main after #9633: before, after, and what it still refuses #9664

For: #9566's two open boxes, now that #9633 (1b1f8f3ad) renders cold code pages off the main thread. The kept-pages-across-a-swap idea (#9631, pull #9632) was dropped: its bench showed no gain. Do not reopen it.

Done looks like:

• [x] bench/results/cold-forge-500.md holds two runs of bun bench/code-pages-at-rate.ts --rate 500 --seconds 20 --warm 0 --crawl 3000 on the same copy: one at 1b1f8f3ad^ (before) and one at main (after), each with served/refused per second, total refused and p95.
• [x] If after refuses no stranger, the file says so and the pull closes nothing else. If it still refuses, the file names how many, in which seconds, and one sentence on why (loop, git pool, or stranger budget), with the next lever to try named as an idea, not built.
• [ ] No code under src/ changes in this pull.

Files: bench/results/cold-forge-500.md only. Risk: bench noise. Run each side twice and report both.

Reviewed pull #9666 at its head: ticked bench/results/cold-forge-500.md holds two runs of bun bench/code-pages-at-rate.ts --rate 500 --seconds 20 --warm 0 --crawl 3000 on the same copy: one at 1b1f8f3ad^ (before) and one at main (after), each with served/refused per second, total refused and p95.; If after refuses no stranger, the file says so and the pull closes nothing else. If it still refuses, the file names how many, in which seconds, and one sentence on why (loop, git pool, or stranger budget), with the next lever to try named as an idea, not built..

Left open after pull #9666 landed: 1 unticked item remains (No code under src/ changes in this pull.). The planner files each as its own issue and closes this one; a person may close it, tick what is done, or say what is left. Until then the crew does not pick it again.

Already done on main in d8a9d5ee6: that commit changes only bench/results/cold-forge-500.md and touches nothing under src/. The next lever it names, the worker pool, is #9671.