feat: add minimal json-rpc node example

Added examples/jsonrpc-get-block.js, demonstrating how to access geth RPC via JSON-RPC using only standard Node.js modules.

examples/jsonrpc-get-block.js

@@ -0,0 +1,60 @@
+#!/usr/bin/env node
+
+/**
+ * Minimal JSON-RPC example that fetches the latest block number
+ * from a running geth node using only Node.js built-ins.
+ *
+ * Usage:
+ *   node examples/jsonrpc-get-block.js
+ *
+ * Optionally override RPC URL:
+ *   RPC_URL=http://127.0.0.1:8545 node examples/jsonrpc-get-block.js
+ */
+
+const http = require("http");
+
+const rpcUrl = process.env.RPC_URL || "http://127.0.0.1:8545";
+const { hostname, port, pathname } = new URL(rpcUrl);
+
+const payload = JSON.stringify({
+  jsonrpc: "2.0",
+  method: "eth_blockNumber",
+  params: [],
+  id: 1,
+});
+
+const options = {
+  hostname,
+  port,
+  path: pathname || "/",
+  method: "POST",
+  headers: {
+    "Content-Type": "application/json",
+    "Content-Length": Buffer.byteLength(payload),
+  },
+};
+
+const req = http.request(options, (res) => {
+  let data = "";
+
+  res.on("data", (chunk) => {
+    data += chunk;
+  });
+
+  res.on("end", () => {
+    try {
+      const json = JSON.parse(data);
+      console.log("RPC response:", json);
+    } catch (e) {
+      console.error("Failed to parse response:", e);
+      console.error("Raw response:", data);
+    }
+  });
+});
+
+req.on("error", (err) => {
+  console.error("Request error:", err);
+});
+
+req.write(payload);
+req.end();