Fix Actor::waitUntilIdle

Actor::waitUntilIdle is not sound because currently it busy loops may causing starvation of the Actor it is waiting for.

If emper is compiled with IO we use an AlarmFuture to wait for a second freeing the worker and then check again.
Otherwise we still busy loop but use the new emper::yieldToAnywhere to free the current worker.

emper/Actor.hpp

@@ -8,6 +8,7 @@
 #include "CallerEnvironment.hpp"
 #include "Fiber.hpp"
 #include "UnboundedBlockingMpscQueue.hpp"
+#include "emper.hpp"
 
 template <typename T>
 class Actor {
@@ -78,8 +79,13 @@ class Actor {
 
 	auto waitUntilIdle(long timeout) -> bool {
 		const auto start = std::chrono::steady_clock::now();
-		const auto deadline = start + std::chrono::milliseconds(timeout);
+		const auto deadline = start + std::chrono::seconds(timeout);
 		while (!(queue.size() == 0 && state.load(std::memory_order_acquire) == Retrieving)) {
+			if constexpr (emper::IO) {
+				emper::sleep(1);
+			} else {
+				emper::yield();
+			}
 			// TODO: The suppressed linter error below may be a false positive
 			// reported by clang-tidy.
 			// NOLINTNEXTLINE(modernize-use-nullptr)