S, T> method
Creates a wrapper that coerces the type of
This soundly converts a StreamSinkTransformer to a
StreamSinkTransformer<S, T>, regardless of its original generic type.
This means that calls to StreamSink.add on the returned sink may throw a
CastError if the argument type doesn't match the reified type of the
static StreamSinkTransformer<S, T> typed<S, T>( StreamSinkTransformer transformer) => transformer is StreamSinkTransformer<S, T> ? transformer : TypeSafeStreamSinkTransformer(transformer);