test(benchmarks): add C#/ASP.NET and TypeScript tasks

Six tasks with hidden checks: ASP.NET validation and 404 handling, C#
cancellation, and TypeScript overlap, deep merge, and debounce fixes, checked
with dotnet run and node --test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/15-csharp-cancellation/hidden/Check/Program.cs

@@ -0,0 +1,20 @@
+using System.Diagnostics;
+using Reports;
+
+var failures = new List<string>();
+var builder = new ReportBuilder();
+var complete = await builder.BuildAsync(new[] { "a", "b" });
+if (complete != "## a\n## b") failures.Add($"unexpected output {complete}");
+using var source = new CancellationTokenSource(TimeSpan.FromMilliseconds(150));
+var watch = Stopwatch.StartNew();
+try
+{
+    await builder.BuildAsync(Enumerable.Range(0, 50).Select(number => number.ToString()), source.Token);
+    failures.Add("no cancellation");
+}
+catch (OperationCanceledException)
+{
+    if (watch.ElapsedMilliseconds > 1000) failures.Add($"cancelled only after {watch.ElapsedMilliseconds} ms");
+}
+foreach (var failure in failures) Console.Error.WriteLine("FAIL " + failure);
+return failures.Count == 0 ? 0 : 1;