Using Serial Differencing Aggregation in .NET

Hey @ximenling20, the AggregationsHelper is missing a method for SerialDifferencing(); I'll add one now.

In the meantime, you can get the value as you have done :+1: You could also get it with

if (item.Aggregations.TryGetValue("serial_diff", out IAggregate aggregate))
{
    var serialDifferencingAggregate = (ValueAggregate) aggregate;
}