* [client] fix busy-loop in network monitor routing socket on macOS/BSD
After system wakeup, the AF_ROUTE socket created by Go's unix.Socket()
is non-blocking, causing unix.Read to return EAGAIN immediately and spin
at 100% CPU filling the log with thousands of warnings per second.
Replace the tight read loop with a unix.Select call that blocks until
the fd is readable, checking ctx cancellation on each 1-second timeout.
Fatal errors (EBADF, EINVAL) now return an error instead of looping.
* [client] add fd range validation in waitReadable to prevent out-of-bound errors
