[EchoServers] improve the callback based echoserver

• Pass the IO results on the stack instead of storing them in the client object.
• Terminate the runtime on quit to print stats.
• Free Client objects.

apps/EchoServer.cpp

@@ -27,6 +27,8 @@ static const std::string HOST = "::";
 static const std::string PORT = "12345";
 static const int BACKLOG = 1024;
 
+static const size_t BUF_SIZE = 1024;
+
 static unsigned int computations_us = 0;
 static unsigned int max_computations_us = 0;
 static float max_computations_probability = -1;
@@ -98,7 +100,7 @@ auto main(int argc, char* argv[]) -> int {
 
 	auto serverFunc = [](int socket) {
 		// NOLINTNEXTLINE(modernize-avoid-c-arrays)
-		char buf[1024];
+		char buf[BUF_SIZE];
 		while (!quit.load(std::memory_order_consume)) {
 			ssize_t bytes_recv = emper::io::recvAndWait(socket, buf, sizeof(buf), 0);
 			if (unlikely(bytes_recv <= 0)) {