Add `db.list` for getting multiple rows by primary key

[aleclarson]

We can't just let db.get take an array of keys, because we want to support array-based keys.

// Order is guaranteed to match the `userIds` array.
const rows = await db.list(t.user, userIds)

This is not simply a shorthand method for db.select(...).where(({ pk }) => pk.in(array)), because the result order is guaranteed to match the input array.

Note: When using this method, the primary key will always be included in the resulting objects.

[aleclarson]

We can probably use WITH ORDINALITY to achieve this without JS massaging 👀

[aleclarson]

We can't just let db.get take an array of keys, because we want to support array-based keys.

Now that we have runtime type information for columns, this isn't a constraint anymore. 👀