Change streams support manual promise-based iteration using `next`, `hasNext` and `tryNext`.  Making the ChangeStream an async iterable would allow idiomatic use in for-await loops.

Additionally, we could use this in conjunction with Readable.from to convert our change stream to a NodeJS readable stream automatically, with full support for resumability (future improvement and not in scope for this work).

Acceptance Criteria

• Implement Symbol.asyncIterator for the ChangeStream class