expose codecs for custom datatypes

[juliusmarminge]

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Describe the proposed feature

Drizzle has a killer feature with customTypes that allows you to use arbitrary datatypes: https://orm.drizzle.team/docs/custom-types. Here's an example of a date column that transforms a mysql date type that's used as a Temporal.PlainDate in JS land:

const temporalDateColumn = customType<{
  data: Temporal.PlainDate;
  driverData: string;
}>({
  dataType: () => "date",
  fromDriver: (value) => Temporal.PlainDate.from(value),
  toDriver: (value) => value.toString(),
});

It would be nice to expose a similar feature in edgedb-js. Brief discussion on Discord: https://discord.com/channels/841451783728529451/1236652945429233664/1236829507911024750

[emrosenf]

This would be useful for encrypting/decrypting data that is encrypted at rest