Add repro test for batching hang issue

Co-authored-by: electricessence <5899455+electricessence@users.noreply.github.com>

Author: Copilot

Open.ChannelExtensions.Tests/HangReproTest.cs

@@ -0,0 +1,58 @@
+using System.Text.Json;
+
+namespace Open.ChannelExtensions.Tests;
+
+public static class HangReproTest
+{
+	/// <summary>
+	/// Reproduction test for the hanging issue described in GitHub.
+	/// This test should fail if the bug exists (by timing out).
+	/// </summary>
+	[Fact]
+	public static async Task MultipleBatchReadersDoNotHang()
+	{
+		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30)); // 30 second timeout
+		var token = cts.Token;
+
+		var counts = new int[5]; // Using 5 tasks instead of 10 for faster testing
+		var tasks = Enumerable.Range(0, 5)
+			.Select(x => Task.Run(async () =>
+			{
+				for (int i = 0; i < 50; i++) // Run 50 iterations instead of infinite
+				{
+					if (token.IsCancellationRequested)
+						break;
+
+					await GetSource()
+						.ToChannel(singleReader: true, cancellationToken: token)
+						.Batch(Random.Shared.Next(15, 30), singleReader: true)
+						.ReadAllAsync(async batch =>
+						{
+							await Task.Delay(Random.Shared.Next(2, 15), token);
+						}, token);
+
+					counts[x] += 1;
+				}
+			}, token)).ToArray();
+
+		// Wait for all tasks to complete or timeout
+		await Task.WhenAll(tasks);
+
+		// Verify all tasks completed at least some iterations
+		Assert.All(counts, count => Assert.True(count >= 40, $"Count was {count}, expected at least 40"));
+	}
+
+	private static async IAsyncEnumerable<int> GetSource([System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
+	{
+		foreach (var value in Enumerable.Range(0, Random.Shared.Next(80, 120)))
+		{
+			if (cancellationToken.IsCancellationRequested)
+				yield break;
+
+			yield return value;
+
+			if (value % Random.Shared.Next(15, 25) == 0)
+				await Task.Delay(Random.Shared.Next(2, 15), cancellationToken);
+		}
+	}
+}