refactor: use more ps$set_values()

[m-muecke]

@mb706 check if you want/like this, this standardises to use more ps$set_values() like in the other mlr3 packages

[mb706]

conflicted about this; the point of $values = list() is that the previous state of $values is overwritten. $set_values() does not change values that are already set; even if it does the same thing, the information that there is no relevant previous state is lost. In reality, we should probably use the init = functionality of the new paradox syntax. Will leave this open for now and think about it