feat: add typescript-async-loaders example

packages/typescript-async-loaders/README.md

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+## TypeScript and async custom loaders
+
+Mocha 11.7.0 added support for Node's experimental [`require_module`](https://nodejs.org/docs/v22.20.0/api/modules.html#loading-ecmascript-modules-using-require) feature, which makes file loading a bit more complicated for Mocha 11. In this example, we showcase using ts-node **and** a custom asynchronous module loader to run a TypeScript test file.
+
+This example shows more integrations than what most projects need. For a more straightforward example, see the [`typescript`](../typescript) sibling package.

packages/typescript-async-loaders/custom-loader.mjs

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+export async function load(url, context, defaultLoad) {
+  if (url.endsWith(".ts")) {
+    console.log("Loaded with custom loader");
+    await new Promise((resolve) => setTimeout(resolve, 1));
+  }
+  return defaultLoad(url, context, defaultLoad);
+}

packages/typescript-async-loaders/package.json

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+{
+  "name": "example-typescript-async-loaders",
+  "version": "1.0.0",
+  "type": "module",
+  "engines": {
+    "node": "^18.18.0 || ^20.9.0 || >=21.1.0"
+  },
+  "scripts": {
+    "test": "NODE_OPTIONS='--loader=ts-node/esm --loader=./custom-loader.mjs' mocha test/**/*.test.ts"
+  },
+  "devDependencies": {
+    "mocha": "^11.7.0",
+    "ts-node": "^10.9.0",
+    "typescript": "^5.0.0",
+    "@types/mocha": "^10.0.0"
+  }
+}

packages/typescript-async-loaders/test/async-loader.test.ts

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+import assert from "assert";
+import { describe, it } from "mocha";
+
+function add(a: number, b: number): number {
+  return a + b;
+}
+
+describe("async loaders", () => {
+  it("should work", () => {
+    assert.strictEqual(add(2, 3), 5);
+  });
+});