fix: finalization/teardown fixes for AsyncGenerators and take (#6062)

* fix: finalization/teardown fixes for AsyncGenerators and take

- Resolves an issue where AsyncGenerators were not properly finalized when an observable result was unsubscribed.
- Resolves another nearly impossible to test scenario that this happens to cover: In the event of an operator like `take()` completing the resulting observable, if an error is thrown in the terminal completion handler, teardown is not invoked, as it would not continue to the next line to call the unsubscribe method of the Subscriber instance. This was resolved by ensuring synchronous calls before the unsubscribe call are called in a try/finally block.

Fixes #5998

* chore: remove unnecessary try/finally