Add docs and further stress tests to the demo

apps/demo/src/components/AsyncLabData.vue

@@ -0,0 +1,16 @@
+<script setup lang="ts">
+const requestedAt = Date.now()
+await new Promise((resolve) => window.setTimeout(resolve, 1_000))
+const resolutionTime = Date.now() - requestedAt
+</script>
+
+<template>
+  <article class="lab-probe lab-probe--ready" data-testid="async-data-ready">
+    <span class="lab-probe__icon" aria-hidden="true">✓</span>
+    <div>
+      <strong>Async payload available</strong>
+      <p>Resolved {{ resolutionTime }} ms after this component mounted.</p>
+    </div>
+  </article>
+</template>
+