Remove sleeps and timed polling from networking

Socket waits now block in select() on the socket plus a wake or cancel
socket (Common/Net/Cancel), so a stop or cancel ends them at once.

- HTTP: cancel flags become net::CancelToken; Connect waits once on all
  addresses, receives wait instead of spinning, no DNS retry sleep.
- Adhoc: the friend finder and adhoc server block on their sockets with
  a wake socket and a deadline; matching runs on a CoreTiming tick
  instead of two threads (savestate section bumped).
- sceNetInet select/poll check without blocking and park the HLE thread,
  re-checked from a CoreTiming event until ready or the emulated
  timeout.
- Vendor the aemu_postoffice client (was a submodule) with no sleeps:
  waits on the socket, close via shutdown and an eventcount, cancelable
  connects, and lock-free session slot claims.
- PortManager waits without a timeout; PSP_InitWait replaces the
  headless boot poll.
- TimeUtil: sleep_us/sleep_ms only outside the core; sleep_precise,
  sleep_random, yield and the Windows timer period are gone.
- Unit test for the socket waits.

Common/Net/Resolve.cpp

@@ -251,7 +251,6 @@ bool DNSResolve(const std::string &host, const std::string &service, addrinfo **
 	int result = getaddrinfo(host.c_str(), servicep, &hints, res);
 	if (result == EAI_AGAIN) {
 		// Temporary failure.  Since this already blocks, let's just try once more.
-		sleep_ms(1, "dns-resolve-poll");
 		result = getaddrinfo(host.c_str(), servicep, &hints, res);
 	}