Enable compile linting and treat warnings as errors

Closes gh-232

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

@@ -26,7 +26,7 @@ class CLR implements CommandLineRunner {
 	@Override
 	public void run(String... args) throws Exception {
 		WebSocketSession session = this.webSocketClient
-			.doHandshake(new MyWebsocketHandler(), null,
+			.execute(new MyWebsocketHandler(), null,
 					URI.create("ws://localhost:%d/echo".formatted(getServerPort())))
 			.get(5, TimeUnit.SECONDS);
 		TextMessage message = new TextMessage("Hello Websocket");