Introduce an array variant for the XGBoost mixer: XGBoostArrayMixer.
Add XGBoostArrayMixer as default mixer. Initial tests suggest runtime should improve without too much loss in accuracy (even then, no actual config space is lost for power users, just default configs change)
Changelog:
XGBoostArrayMixer.XGBoostArrayMixeras default mixer. Initial tests suggest runtime should improve without too much loss in accuracy (even then, no actual config space is lost for power users, just default configs change)