Fix CPU hang in BatchingChannelReader.WaitToReadAsyncCore

The issue was that after Task.WhenAny completed, the code did not await
the source task before looping. This caused a tight CPU-consuming loop
when the source channel was closed but the buffer was empty, as the
closed source would immediately return a completed ValueTask on each
WaitToReadAsync call.

The fix properly awaits the source task after WhenAny to check its
completion status, preventing the tight loop. This matches the pattern
used in the base BufferingChannelReader class.

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

Author: Copilot

Open.ChannelExtensions/Readers/BatchingChannelReader.cs

@@ -245,13 +245,20 @@ protected override async ValueTask<bool> WaitToReadAsyncCore(
 		}
 
 		// WhenAny will not throw when a task is cancelled.
-		await Task.WhenAny(s.AsTask(), b).ConfigureAwait(false);
+		Task<bool> sTask = s.AsTask();
+		await Task.WhenAny(sTask, b).ConfigureAwait(false);
 		if (b.IsCompleted) // Assuming it was bufferWait that completed.
 		{
 			await tokenSource.CancelAsync().ConfigureAwait(false);
 			return await b.ConfigureAwait(false);
 		}
 
+		// Await the source task to check if it completed and get its result
+		// This prevents a tight loop when the source is closed
+		await sTask.ConfigureAwait(false);
+		if (b.IsCompleted)
+			return await b.ConfigureAwait(false);
+
 		TryPipeItems(false);
 
 		if (b.IsCompleted || token.IsCancellationRequested)