Supervises an explicitly selected, immutable HTTP/1 and HTTP/2 pool family.

{HTTP.Runtime.Pool,
 name: "api",
 http1: [max_idle_per_key: 1, max_idle: 8],
 http2: [max_connections: 1, max_streams: 16]}

HTTP.fetch(url, pool: "api")

reference/1 captures a generation for reuse across requests. Names are atoms or strings registered without converting external strings into atoms. Families restart together: old references fail with :stale_pool and never fall back. HTTP/1 selection enables reuse. Explicit http1_reuse: false, retention above the instance policy, managed scopes, HTTP/3 and automatic negotiation are rejected before dialing. HTTP/2 selection requires reusable pool identities.