[FEATURE]: Improve ergonomics of type-safety of PgEnum

### Describe what you want

Here's the user story of writing a new `PgEnum`:

1. Write a simple `pgEnum`:


Cool, simple, works, compiles. But the type is only inferred here, rather than checked / enforced. So let's try to add a `satisfies`:


Ah, `PgEnum` requires a type parameter. Let's add one:


Green again. But now I've duplicated the enum values into both the enum definition and into the type-check. Can we DRY?


Not quite, the type parameter doesn't accept `readonly`. Let's find [a trick on Stack Overflow](https://stackoverflow.com/a/43001581):


Great, back to green. But this feels very awkward / boilerplate...? Is it not possible to have either `satisfies PgEnum;` (similar to `PgTable`), without specifying a type parameter, or have the type parameter accept `readonly` so that it can use `typeof` an `as const` array?