createInstrumentedHttpClient function
Creates an HttpClient whose connectionFactory records DNS + TCP connect
durations into the current HttpClientConnectTiming zone value.
Must not use the public HttpClient() factory: that re-enters
HttpOverrides.current and infinite-loops when global tracking overrides
(e.g. TrackedHttpOverrides) are installed. A fresh root HttpOverrides
builds the real client without going through the global override.
Implementation
HttpClient createInstrumentedHttpClient({SecurityContext? context}) {
final client = _RootHttpOverrides().createHttpClient(context);
applyInstrumentedConnectionFactory(client);
return client;
}