fit_tr_val's train_test_split had no random_state, so val_split=float
picked a different split every run; occasionally the split produced a
posterior distribution that made abstention's temperature-scaling
L-BFGS optimizer diverge to NaN. Threaded random_state through the
base class and all four calibrator subclasses, and pinned the test to
a seed confirmed stable across repeated runs.
Alejandro Moreo Fernandez
Alejandro Moreo