feat: add MCP tasks support to example server

Add task-based execution support for the longRunningOperation tool,
demonstrating the MCP Tasks protocol. Changes include:

- Add InMemoryTaskStore and InMemoryTaskMessageQueue
- Declare tasks capability with list, cancel, and tool call support
- Extract runLongOperation helper for background task execution
- Add task status updates and cancellation checking during long operations
- Update SDK to 1.26.0 for tasks support

Author: Guro

package-lock.json

@@ -24,7 +24,7 @@
   },
   "dependencies": {
     "@modelcontextprotocol/ext-apps": "^1.0.1",
-    "@modelcontextprotocol/sdk": "1.24.2",
+    "@modelcontextprotocol/sdk": "1.26.0",
     "@modelcontextprotocol/server-budget-allocator": "^1.0.1",
     "@modelcontextprotocol/server-cohort-heatmap": "^1.0.1",
     "@modelcontextprotocol/server-customer-segmentation": "^1.0.1",