Add Span Loop Extensions

[jeremyknight-me]

Quick code sample would look like:

void Main()
{
    var list = Enumerable.Range(0, 100).ToList();
    list.SpanIterate(l => { Console.WriteLine(l); });
}

internal static class MyExtensions 
{
    /// <summary>ONLY USE ON LISTS THAT CANNOT CHANGE DURING PROCESSING</summary>
    internal static void SpanIterate<T>(this List<T> list, Action<T> action) {
        var span = CollectionsMarshal.AsSpan(list);
        for (var i = 0; i < span.Length; i++) {
            action(span[i]);
        }
    }

    internal static void SpanIterate<T>(this IReadOnlyList<T> list, Action<T> action)
    {
        var span = CollectionsMarshal.AsSpan(list.ToList());
        for (var i = 0; i < span.Length; i++)
        {
            action(span[i]);
        }
    }
}