HistoricalSchedulerBase
Base class for historical schedulers, which are virtual time schedulers that use  DateTimeOffset for absolute time and  TimeSpan for relative time.
            
                using System.Collections.Generic;
using System.Runtime.CompilerServices;
namespace System.Reactive.Concurrency
{
    public abstract class HistoricalSchedulerBase : VirtualTimeSchedulerBase<DateTimeOffset, TimeSpan>
    {
        protected HistoricalSchedulerBase()
            : base(DateTimeOffset.MinValue, (IComparer<DateTimeOffset>)Comparer<DateTimeOffset>.Default)
        {
        }
        protected HistoricalSchedulerBase(DateTimeOffset initialClock)
            : base(initialClock, (IComparer<DateTimeOffset>)Comparer<DateTimeOffset>.Default)
        {
        }
        [System.Runtime.CompilerServices.NullableContext(1)]
        protected HistoricalSchedulerBase(DateTimeOffset initialClock, IComparer<DateTimeOffset> comparer)
            : base(initialClock, comparer)
        {
        }
        protected override DateTimeOffset Add(DateTimeOffset absolute, TimeSpan relative)
        {
            return absolute.Add(relative);
        }
        protected override DateTimeOffset ToDateTimeOffset(DateTimeOffset absolute)
        {
            return absolute;
        }
        protected override TimeSpan ToRelative(TimeSpan timeSpan)
        {
            return timeSpan;
        }
    }
}