Allow transformer to reject inputs about featran HOT 3 CLOSED

Reject meaning zero out or don't output the vector entirely? This for cases like outliers or one hot encoded enums where the aggregator doesn't have an entry?

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Not zero, but some separate output indicating some error, e.g. out of bound, outlier. Users can choose to keep the output (likely zeroed out) or filter the entire records out if error exists.
We can represent FeatureBuilder output something like a Try[T] or cats Validation.

from featran.

I see, makes sense. Exposing errors and allowing people to decide what to do with them is always a good path. If nothing else there will be cases where the function that is passed to the transformer will hit malformed data.

from featran.