Returning a Reader ends up with a really weird user experience where you
have to make sure to drop it before making any other calls and it has to
internally fast forward to the end of the data even if the user drops it
early. Simply taking a Writer that all data is pushed into is
sigificantly more straightforward.
It doesn't make any sense to limit lazy queries to statments *prepared*
inside a transaction. We really only care that we're in a transaction
when the statement is executed. This does introduce a new runtime error
if a statement prepared on connection A is executed on a transaction
prepared on connection B, but I don't think anyone will *ever* run into
that.
