feat: implement resource update notifications (#264)

This enables servers to notify clients when specific resources are updated,
allowing clients to react to individual resource changes rather than just
list changes.

- Add ResourcesUpdatedNotification schema with uri field
- Add METHOD_NOTIFICATION_RESOURCES_UPDATED constant
- Implement notifyResourcesUpdated() methods in McpAsyncServer and McpSyncServer
- Add client-side support for resource update consumers and handlers
- Client automatically reads updated resource content when notification received
- Add tests for both async and sync server implementations

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

mcp/src/main/java/io/modelcontextprotocol/server/McpSyncServer.java

@@ -141,6 +141,13 @@ public class McpSyncServer {
 		this.asyncServer.notifyResourcesListChanged().block();
 	}
 
+	/**
+	 * Notify clients that the resources have updated.
+	 */
+	public void notifyResourcesUpdated(McpSchema.ResourcesUpdatedNotification resourcesUpdatedNotification) {
+		this.asyncServer.notifyResourcesUpdated(resourcesUpdatedNotification).block();
+	}
+
 	/**
 	 * Notify clients that the list of available prompts has changed.
 	 */