types

Types shared across the postgres interfaces. The value model (`pg-value`) and the error model (`error`, `db-error`) live here so that `query` and `prepared` `use` the *same* types. That matters for the component-model `(implements ..)` mechanism: a host can route each labeled `query`/`prepared` import to its own credentialed connection, and the values and errors flowing through one label unify with the (unlabeled) interfaces because they all reference this one `types` package.