Heteroscedastic Gaussian process regression.
Calls hetGP::mleHetGP() from package hetGP.
Predictions return the posterior mean and the square root of the full
predictive variance (sd2 + nugs) as standard error.
noiseControl and settings are represented by explicit learner
hyperparameters tagged "noise_control" and "settings", respectively.
The wrapper reconstructs the nested lists expected by hetGP::mleHetGP()
internally.
Creates a new instance of this learner.