feat(sse): expand accepted HTTP status codes for SSE stream connection

Accept HTTP status codes 200, 201, 202, and 206 as valid responses
for SSE stream connection. Improves error message to include actual
status code. Removes unused main method.

Resolves #68

Author: tzolov

mcp/src/main/java/org/springframework/ai/mcp/client/transport/FlowSseClient.java

@@ -198,39 +198,14 @@ public void onComplete() {
 				info -> subscriberFactory.apply(lineSubscriber));
 
 		future.thenAccept(response -> {
-			if (response.statusCode() != 200) {
-				throw new RuntimeException("Failed to connect to SSE stream: " + response.statusCode());
+			int status = response.statusCode();
+			if (status != 200 && status != 201 && status != 202 && status != 206) {
+				throw new RuntimeException("Failed to connect to SSE stream. Unexpected status code: " + status);
 			}
 		}).exceptionally(throwable -> {
 			eventHandler.onError(throwable);
 			return null;
 		});
 	}
 
-	// public static void main(String[] args) {
-
-	// FlowSseClient sseClient = new FlowSseClient(
-	// HttpClient.newBuilder().connectTimeout(Duration.ofSeconds(10)).build());
-
-	// var eventHandler = new SSEEventHandler() {
-	// @Override
-	// public void onEvent(SSEEvent event) {
-	// System.out.println("Received event: " + event);
-	// }
-
-	// @Override
-	// public void onError(Throwable error) {
-	// System.out.println("Error: " + error);
-	// }
-	// };
-	// sseClient.subscribe("http://localhost:8080/sse", eventHandler);
-
-	// try {
-	// Thread.sleep(100000);
-	// }
-	// catch (InterruptedException e) {
-	// e.printStackTrace();
-	// }
-	// }
-
 }