internal StreamOperator(Stream <TIn> inner, IPersistableOperator <TIn, TOut> ipo, IReadOnlyDictionary <string, object> sd) : base(sd)
 {
     _inner = inner;
     _ipo   = ipo;
 }
 internal StreamOperator(Stream <TIn> inner, IPersistableOperator <TIn, TOut> ipo)
 {
     _inner = inner;
     _ipo   = ipo;
 }