addr_map_ only accepted IP literals as mapped values; a non-IP value was
passed as the `ip` argument and rejected by getaddrinfo's AI_NUMERICHOST
path. The lookup in ClientImpl::create_client_socket and
WebSocketClient::connect now checks the mapped value with
detail::is_ip_address: IP literals keep the existing AI_NUMERICHOST path,
while hostnames are passed as the connect host so they get resolved.
host_ is never touched, so it keeps supplying the Host header and SNI in
both cases.
is_ip_address() moved into the non-SSL detail block so that both client
code paths can use it without CPPHTTPLIB_SSL_ENABLED.
This also fixes the documented Unix domain socket client example, where
the mapped value is a socket path: it previously took the AI_NUMERICHOST
path and never reached the AF_UNIX branch in create_socket.
Replace the hand-built upgrade request string in
perform_websocket_handshake with the same Request,
write_request_line, and check_and_write_headers path used by
ClientImpl::open_stream. Add WebSocketClient::prepare_default_headers
to inject Host and User-Agent defaults; protocol-mandatory headers
(Upgrade, Connection, Sec-WebSocket-Key/Version) are always
overwritten.
Kim, Hyuk