Refactor BatchingChannelReader timeout handling and improve test reliability

Author: electricessence

Open.ChannelExtensions.Tests/HangReproTest.cs

@@ -26,10 +26,8 @@ public static async Task MultipleBatchReadersDoNotHang()
 					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);
+						.WithTimeout(TimeSpan.FromMilliseconds(100))
+						.ReadAllAsync(async batch => await Task.Delay(Random.Shared.Next(2, 15), token), token);
 
 					counts[x] += 1;
 				}

Open.ChannelExtensions/Readers/BatchingChannelReader.cs

@@ -95,10 +95,14 @@ public BatchingChannelReader<T, TBatch> WithTimeout(long millisecondsTimeout)
 
 	private void TryUpdateTimer(long timeout)
 	{
+		var t = _timer;;
+		if (t is null) return;
+
 		try
 		{
-			bool? ok = _timer?.Change(timeout, 0);
-			Debug.Assert(ok ?? true);
+			t.Change(timeout, 0);
+			// bool? ok = t.Change(timeout, 0);
+			// Debug.Assert(ok ?? true);
 		}
 		catch (ObjectDisposedException)
 		{