tvOS logs flood with "HTTP client drain timed out" / "close deferred"
warning pairs after every Plex endpoint race, and each sweep leaks the
losing probes' sockets for the OS connect timeout (~75 s of SYN
retries on Darwin).
A request stuck in TCP connect cannot be aborted: package:http's
IOClient only registers the abort handler once openUrl completes, so
the graceful drain never finishes and ManagedHttpClient defers the
inner close that would have reclaimed the socket.
Fix at both layers: every IOClient now gets an explicit
HttpClient.connectionTimeout matching MediaServerTimeouts.connect, and
ManagedHttpClient gains an opt-in forceCloseOnDrainTimeout escalation
used by all dart:io-backed clients — close(force: true) promptly fails
in-flight requests, unlike the native-callback clients (CupertinoClient)
the deferral exists for.
close#1972
edde746