feat: support interruptible transactions

[pmorris-dev]

Also added support for rolling back active transactions (interruptible ones and regular ones), when the app is about to exit.

[jjhafer]

The API looks straightforward and easy to use. I hadn't really thought of this use-case as an "interruptible" transaction that requires a "continue", but more of the ability to perform logic and reads during a transaction. My initial hang-up was probably recency bias where statements are passed in via a closure or callback like:

db.transaction({ tx in
    tx.executeSomeWrite()
    <some logic>
    tx.executeSomeRead()
    <some logic>
    tx.executeSomeWrite()
    tx.commit() or tx.rollback()
})

But I don't know if the above is a good pattern in Rust. Anyway, the clear API you wrote seems like a good place to start. Thanks for the good driving directions!