Currently, the async iterator in abstract cursor can return an AsyncGenerator when using native promises or an AsyncIterator when using 3rd-party promises. For the sake of consistency, we should change the return type to always be AsyncGenerator since it's a stricter type than AsyncIterator.

When we remove the custom promise version of the async generator we can update the return type to be AsyncGenerator.

Acceptance Criteria

• change the return type of the asyncIterator symbol in abstract cursor to be AsyncGenerator