Extract design information from an stpm2/gsm object and newdata for use in C++
gsm_design(object, newdata, newdata0 = NULL, t0 = NULL, inflate = 100)
list that can be read by `gsm ssim::read_gsm(SEX args)` in C++
stpm2/gsm object
list or data-frame used for evaluation
list or data-frame used for evaluation at the entry time
possible delayed entry time (numeric scalar)
double value to inflate minimum and maximum times for root finding