wip: Support binary auto req/res.

[connyay]

Currently broken without cloudflare/workerd#6738

[guybedford]

Approval for when ready.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 2 untouched benchmarks

---

_{Comparing connyay:cjh-bin-setautoresponse (dd8fbea) with main (417576c)}