src/transformers/generation/beam_constraints.py/PhrasalConstraint/copy
class PhrasalConstraint:    def copy(self, stateful=False):
        new_constraint = PhrasalConstraint(self.token_ids)

        if stateful:
            new_constraint.seq_len = self.seqlen
            new_constraint.fulfilled_idx = self.fulfilled_idx
            new_constraint.completed = self.completed

        return new_constraint