Implement BYO zod v3 or v4

Following recommendations from https://zod.dev/library-authors

Author: fredericbarthelet

examples/simple-server/package.json

@@ -13,7 +13,7 @@
     "@modelcontextprotocol/sdk": "^1.22.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
-    "zod": "^3.25.0"
+    "zod": "^4.1.13"
   },
   "devDependencies": {
     "@types/express": "^5.0.0",

examples/simple-server/server.ts

@@ -1,7 +1,7 @@
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
 import express, { Request, Response } from "express";
 import { randomUUID } from "node:crypto";
-import { z } from "zod";
+import * as z from "zod";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import {
   CallToolResult,