RFC 9220 — Bootstrapping WebSockets with HTTP/3.

RFC 9220 reuses the RFC 8441 extended CONNECT pattern on top of HTTP/3 streams. The only wire-level differences (capsule framing, SETTINGS_ENABLE_CONNECT_PROTOCOL carried in H3 settings) live in the embedder's H3 stack (erlang_quic's h3 module). From this module's point of view the pseudo-header validation and response shape are identical to HTTP/2 — so we reuse ws_h2_upgrade under the hood and expose the name for discoverability.