refactor: downgrade unhandled notification logging from error to warn

- Change logger.error() to logger.warn() for unhandled notification methods
- Log full notification object instead of just method name for better context
- Affects McpClientSession, McpServerSession, and McpStreamableServerSession

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

mcp/src/main/java/io/modelcontextprotocol/spec/McpClientSession.java

@@ -221,7 +221,7 @@ private Mono<Void> handleIncomingNotification(McpSchema.JSONRPCNotification noti
 		return Mono.defer(() -> {
 			var handler = notificationHandlers.get(notification.method());
 			if (handler == null) {
-				logger.error("No handler registered for notification method: {}", notification.method());
+				logger.warn("No handler registered for notification method: {}", notification);
 				return Mono.empty();
 			}
 			return handler.handle(notification.params());

mcp/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java

@@ -294,7 +294,7 @@ private Mono<Void> handleIncomingNotification(McpSchema.JSONRPCNotification noti
 
 			var handler = notificationHandlers.get(notification.method());
 			if (handler == null) {
-				logger.error("No handler registered for notification method: {}", notification.method());
+				logger.warn("No handler registered for notification method: {}", notification);
 				return Mono.empty();
 			}
 			return this.exchangeSink.asMono().flatMap(exchange -> handler.handle(exchange, notification.params()));

mcp/src/main/java/io/modelcontextprotocol/spec/McpStreamableServerSession.java

@@ -197,7 +197,7 @@ public Mono<Void> accept(McpSchema.JSONRPCNotification notification) {
 			McpTransportContext transportContext = ctx.getOrDefault(McpTransportContext.KEY, McpTransportContext.EMPTY);
 			McpNotificationHandler notificationHandler = this.notificationHandlers.get(notification.method());
 			if (notificationHandler == null) {
-				logger.error("No handler registered for notification method: {}", notification.method());
+				logger.warn("No handler registered for notification method: {}", notification);
 				return Mono.empty();
 			}
 			McpLoggableSession listeningStream = this.listeningStreamRef.get();