Provide customizable transactional interface

[DXist]

Hi!

Thank you for your efforts on this project!

My question is whether it's possible to provide customizable transactional interface? For example via trait and its default implementation. It could be applied as a model state type parameter.

I'm experimenting with this sqlx wrapper to model data on top of CockroachDB. I want to support transaction retry mechanism that uses retry savepoints.