Add UWS_REMOTE_ADDRESS_USERSPACE macro for userspace remote address caching

[Copilot]

When UWS_REMOTE_ADDRESS_USERSPACE is defined, the remote IP is cached in per-socket data at connection time (from the on_open arguments) rather than retrieved via syscall on each getRemoteAddress() call.

Changes

• AsyncSocketData — adds char remoteAddress[16] and int remoteAddressLength fields, guarded by #ifdef UWS_REMOTE_ADDRESS_USERSPACE
• HttpContext on_open — copies ip/ip_length into the socket ext immediately after placement-new; validates 0 < ip_length <= 16, sets length to 0 otherwise
• AsyncSocket::getRemoteAddress() — returns a string_view into the cached socket data under the macro; falls back to us_socket_remote_address() when undefined

// With -DUWS_REMOTE_ADDRESS_USERSPACE:
// IP is captured once on connect from on_open args, stored in AsyncSocketData.
// getRemoteAddress() reads directly from socket ext — no syscall.

// Without the macro: existing behavior unchanged.

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