Enable compile linting and treat warnings as errors

Closes gh-232

framework/websocket-stomp/src/main/java/com/example/websocket/stomp/CLR.java

@@ -31,7 +31,7 @@ class CLR implements CommandLineRunner {
 	public void run(String... args) throws Exception {
 		MyStompHandler handler = new MyStompHandler();
 		StompSession stompSession = this.webSocketStompClient
-			.connect("ws://localhost:%d/stomp".formatted(getServerPort()), handler)
+			.connectAsync("ws://localhost:%d/stomp".formatted(getServerPort()), handler)
 			.get(5, TimeUnit.SECONDS);
 
 		stompSession.subscribe("/topic/greetings", handler);