The documentation states that you can pass custom type processors to
query objects. See:
https://node-postgres.com/features/queries#types
This didn't actually work. This commit adds an initial implementation
of per-query type-parsing. Caveats:
* It does not work with pg-native. That would require a separate pull
request to pg-native, and a rather significant change to how that
library handles query results.
* Per-query types do not "inherit" from types assigned to the Client,
ala TypeOverrides.
566058de17