read-values dispatches to the ReadValues protocol. It returns an
iterator via an ObjectReader derived from the supplied mapper.
The returned iterator is reified in a manner similar to Eduction to
support reduction and sequence construction over it.

write-values relies on two protocols - WriteValues for the output
destination, similarly to WriteValue, and WriteAll for the type being
written, which can be an array or an Iterable.
It writes an array or iterable to destination via a SequenceWriter.
Importantly, write-values distables automatic flushing on serialization
to get good performance.

…streaming