#[require_transactional] annotation

[xlc]

Due to the limitation of current transactional overlay storage, it is recommended to not have too many nested with_transaction calls #6269 (comment).

So we end up many calls that have rollback after storage modification, expected to only be called within with_transaction.

Currently the only way to ensure those calls are used correctly is manual review, which are error-prone.

I would like to suggest a #[require_transactional] annotation, on release build, does nothing, but on debug std build / unit test, assert it is called within with_transaction.