Address code review feedback

- Remove unused System.Text.Json import from test
- Use consistent attribute style in test
- Add clarifying comment explaining the buffer completion check

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

Author: Copilot

Open.ChannelExtensions.Tests/HangReproTest.cs

@@ -1,4 +1,4 @@
-using System.Text.Json;
+using System.Runtime.CompilerServices;
 
 namespace Open.ChannelExtensions.Tests;
 
@@ -42,7 +42,7 @@ await GetSource()
 		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)
+	private static async IAsyncEnumerable<int> GetSource([EnumeratorCancellation] CancellationToken cancellationToken = default)
 	{
 		foreach (var value in Enumerable.Range(0, Random.Shared.Next(80, 120)))
 		{

Open.ChannelExtensions/Readers/BatchingChannelReader.cs

@@ -256,6 +256,8 @@ protected override async ValueTask<bool> WaitToReadAsyncCore(
 		// 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);
+		// Check if buffer completed while we were waiting (e.g., timeout forced a batch)
+		// If so, return immediately without trying to pipe more items
 		if (b.IsCompleted)
 			return await b.ConfigureAwait(false);