nerdctl as API (for unit/e2e tests, etc.)

Hopefully this is not a totally bonkers feature request 🤓 ...

When dealing with container-related unit tests or end-to-end tests, in the existing Docker world we thankfully have [ory/dockertest](https://github.com/ory/dockertest). dockertest predates the official go Docker client and thus talks JSON directly to the Docker daemon's API endpoint. Even without dockertest there's still the go Docker client API with higher-level API elements for easily getting containers to run.

Now, with the containerd go client API, we're back to riding the hot engine directly ... which is a P.I.T.A. causing lots of raw burns.

nerdctl exactly is the missing abstraction layer, but at the moment is a CLI binary-onle approach, if I'm not mistaken and overlooking something important here. Do you think it possible to use the nerdctl module not as a standalone binary but instead as a high-level containerd API?

Maybe that is possible already and it would just need some documentation with an example how to use nerdctl (the API) in the unit tests of other modules?