Adding Merge and Split for System.Threading.Channels

[kdcllc]

https://deniskyashif.com/2019/12/08/csharp-channels-part-1/

static ChannelReader<T> Merge<T>(params ChannelReader<T>[] inputs)
{
    var output = Channel.CreateUnbounded<T>();

    Task.Run(async () =>
    {
        async Task Redirect(ChannelReader<T> input)
        {
            await foreach (var item in input.ReadAllAsync())
                await output.Writer.WriteAsync(item);
    	}
            
        await Task.WhenAll(inputs.Select(i => Redirect(i)).ToArray());
        output.Writer.Complete();
    });

    return output;
}

static IList<ChannelReader<T>> Split<T>(ChannelReader<T> ch, int n)
{
    var outputs = new Channel<T>[n];

    for (int i = 0; i < n; i++)
        outputs[i] = Channel.CreateUnbounded<T>();

    Task.Run(async () =>
    {
        var index = 0;
        await foreach (var item in ch.ReadAllAsync())
        {
            await outputs[index].Writer.WriteAsync(item);
            index = (index + 1) % n;
        }

        foreach (var ch in outputs)
            ch.Writer.Complete();
    });

    return outputs.Select(ch => ch.Reader).ToArray();
}

https://btburnett.com/csharp/2019/12/01/iasyncenumerable-is-your-friend.html