M0.4 Benchmark: SharedArrayBuffer zero-copy vs postMessage in workers

[melvincarvalho]

Part of #1 (M0).

Goal

Compare distributing verification work to workers via SharedArrayBuffer (zero-copy) versus postMessage with transferables.

Benchmark / acceptance

• Effective verifies/sec at N workers for both transports.
• Quantify the copy/messaging overhead SAB removes.
• Decision: is SAB worth requiring cross-origin isolation (COOP/COEP via coi-serviceworker on gh-pages) for v1, or do we ship without it first?

Notes

SAB needs COOP/COEP, which gh-pages cannot set as headers (service-worker workaround exists). This benchmark decides whether that complexity is justified.