fix: drop perp-oi + DYNAMIC_SERVER_USAGE 500 on draft bench pages

[Flotapponnier]

Summary

• Drop perp-open-interest bench (multi-chain OI aggregation structurally biased)
• Remove noStore()/unstable_noStore() calls after unstable_cache — Next.js 15 throws DYNAMIC_SERVER_USAGE when this sequence happens, causing 500 on all draft/awaiting bench pages

Test plan

• Draft bench pages (perp-exit-custody, swellchain-rpc, etc.) return 200 on staging
• Live bench pages still 200