Simplify inner the structures of forest.ARFClassifier and forest.ARFRegressor by removing redundant class hierarchy. Simplify how concept drift logging can be accessed in individual trees and in the forest as a whole.
Fix a bug in tree.splitter.NominalSplitterClassif that generated a mismatch between the number of existing tree branches and the number of tracked branches.
Fix a bug in tree.ExtremelyFastDecisionTreeClassifier where the split re-evaluation failed when the current branch's feature was not available as a split option. The fix also enables the tree to pre-prune a leaf via the tie-breaking mechanism.