Add simple test app

test/.npmrc

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+registry=https://registry.npmjs.org/
+@lightningchart:registry=https://registry.npmjs.org/

test/index.js

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+import express from "express";
+import { PNG } from "pngjs";
+import { lightningChart, renderToPNG } from "@lightningchart/lcjs-headless";
+import { flatThemeLight } from "@lightningchart/lcjs-themes";
+
+const app = express();
+const port = 3000;
+
+app.get("/", (req, res) => {
+  const lc = lightningChart({
+    // Valid until 8/6/2024
+    license:
+      "0002-n6Q3wipxRCPK7PHm1Z1p6PdhNNqeKwClN/s+aUwl3vT54A0lse0e9Ryv9JY4YzR8avVBVjTpcgbR7Q8DS2egZAHn-MEUCIQC87Etz4Jn4NLyctnrTCjVOHKsy7VSxa99DG6arbb1RfgIgZKtGhZpmATUsBZ6fkq834+Sq137gFyv7lsz3OVndGvA=",
+    licenseInformation: {
+      appTitle: "LightningChart JS Trial",
+      company: "LightningChart Ltd.",
+    },
+  });
+  const chart = lc.ChartXY({ theme: flatThemeLight });
+  const chartOutput = renderToPNG(chart, 800, 640);
+  const outputBuff = PNG.sync.write(chartOutput);
+  res.setHeader("Content-Type", "image/png");
+  res.setHeader("Content-Length", outputBuff.length);
+  res.send(outputBuff);
+});
+
+app.listen(port, () => {
+  console.log(`Example app listening at http://localhost:${port}`);
+});