fit_cond_density_quantile
                        Estimate conditional density pi(y|x) via
                        quantile process + quotient estimator
fit_missingness_propensity
                        Fit missingness propensity model P(delta=1 | X)
                        from pooled data
generate_clustered_mar
                        Simulate clustered continuous outcomes with
                        covariate-dependent MAR missingness
hcp_conformal_region    HCP conformal prediction region with repeated
                        subsampling and repeated data splitting
hcp_predict_targets     HCP prediction wrapper for multiple
                        measurements with optional per-patient
                        Bonferroni
plot_hcp_intervals      Plot HCP prediction intervals (band vs
                        covariate or intervals by patient)
