fix: increase maximum test duration from 5 to 20 seconds

src/routes/+page.svelte

@@ -6,7 +6,7 @@
 
 	Chart.register(...registerables);
 
-	const MaxTestDurationSec = 5;
+	const MaxTestDurationSec = 20;
 
 	let currentBandwidth = $state(0);
 	let accumulatedBandwidth = 0;