5.20.0
(feat): Add opt-in, platform-guarded TCP keepalive for the generated default HTTP
transport. Enable it via the new tcp_keepalive custom config
(enabled, idle_seconds, interval_seconds, count); it is disabled by
default so existing generated output is unchanged. When enabled, the default
httpx transport applies SO_KEEPALIVE plus the platform’s idle/interval/count
knobs (with a macOS TCP_KEEPIDLE -> TCP_KEEPALIVE fallback and guards for
older/minimal platforms) so long, non-streaming requests survive
idle-connection reaping by a firewall/load balancer/NAT. A user-supplied
httpx_client or a custom_transport http_client always takes precedence
over the keepalive default. Opting in requires httpx>=0.25.
(fix): Fix the async default client dropping a custom_transport http_client.
_make_default_async_client now threads the supplied transport through to the
underlying httpx.AsyncClient (the httpx-aiohttp path remains a documented
no-op, since aiohttp manages its own connector).