Docs: Transaction type is 'unrolled', making types look much more complex

As an example `signTransactionMessageWithSigners` returns the type `Promise`

`SendableTransaction` is exported: `export type SendableTransaction = FullySignedTransaction & TransactionWithinSizeLimit`

[In our docs](https://www.solanakit.com/api/functions/signTransactionMessageWithSigners#returns) this shows as:

```ts
Promise & TransactionWithLifetime>
```

This looks much more complex, because the `Transaction` type has been unnecessarily unrolled to the fields that it contains. `Transaction` is a core type and makes sense to keep as-is in our documentation.

I'm not sure if this is a Fumadocs bug or something we can configure.