New integration testing strategy to verify re-exports and `into_model`

While attempting to use `types` to implement a production client in `bdk` I found that error types were not re-exported. Somewhat related; in `verify`  we currently only verify that a test `foo_bar` exists for RPC method `foobar` but we do not verify that `into_model` is tested.

I have a patch in development to improve this.