Benchmarking two different approaches to IAsyncEnumerable.Switch, forcing non-synchronous ValueTask completion

BenchmarkAsyncSwitchBlocking.cs

[MemoryDiagnoser]
public class SwitchWithBlockingSources
{
    public readonly static IAsyncEnumerable<IAsyncEnumerable<int>> source = AsyncEnumerable
        .Range(0, 1000)
        .SelectAwait(async i =>
        {
            await Task.Yield();
            return AsyncEnumerable
                .Range(0, 1000)
                .SelectAwait(async i =>
                {
                    await Task.Yield();
                    return i;
                });
        });

    [Benchmark]
    public async ValueTask<int> IterativeSingleLogicalThread()
    {
        return await source.Switch().LastAsync();
    }

    [Benchmark]
    public async ValueTask<int> ConcurrentLogicalThreads()
    {
        return await source.Switch2().LastAsync();
    }
}