[BUG]: `getSQL` on subquery not working

### What version of `drizzle-orm` are you using?

^0.30.1

### What version of `drizzle-kit` are you using?

_No response_

### Describe the Bug

The following code does not work:
```ts
const inner = db
.$with("inner")
.as(
db
.select()
.from(someTable)
);

const s = sql.empty();
s.append(inner.getSQL());
```

Currently when running this code I receive the following error:
`TypeError: inner.getSQL is not a function`

### Expected behavior

`getSQL` to be implemented to avoid the runtime error.

Given their is a type definition for it, it seems unintentional this method is missing at runtime.

### Environment & setup

_No response_

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Thanks for all your work on Drizzle ORM. It's such a great tool!