Force the second absorption delay longer than the first
Source:R/addSecondAbsorption.R
convertAbsForceLongerDelay.RdReparameterizes a double-absorption model so the second path's lag is estimated as a positive increment over the first path's lag (`Tlag2 = Tlag1 + diffTlag2`), matching Monolix's "force delay2 longer than delay1" models. Both paths must have lag times and the model must not already be sequential.