fix close_wait and tomcat connection keeps growing

Author: taobaorun

mcp-spring/mcp-spring-webmvc/src/main/java/io/modelcontextprotocol/server/transport/WebMvcSseServerTransportProvider.java

@@ -263,10 +263,13 @@ private ServerResponse handleSseConnection(ServerRequest request) {
 			logger.debug("Creating new SSE connection for session: {}", sessionId);
 			sseBuilder.onComplete(() -> {
 				logger.debug("SSE connection completed for session: {}", sessionId);
+				// explicitly close the session when the SSE connection is completed
+				session.close();
 				sessions.remove(sessionId);
 			});
 			sseBuilder.onTimeout(() -> {
 				logger.debug("SSE connection timed out for session: {}", sessionId);
+				session.close();
 				sessions.remove(sessionId);
 			});
 			this.sessions.put(sessionId, session);