feat: add conformal Bayesian prediction

[lsorber]

Adds asymmetric conformal Bayesian prediction for both classification and regression.

Details:

• Asymmetric means we estimate the positive and negative residual quantiles separately.
• Bayesian means the nonconformity measure is that of Gaussian Processes.
• To construct the confidence interval we apply linear quantile regression on the leave-one-out residuals given the leave-one-out nonconformity measures.

[lsorber]

Test set performance on the Ames housing dataset: