Is there a package-level smart service for Automated Testing for Expression Rules

 As far as I know the smart services available for expression rules testing is for all appian exression rules or an application’s. As a workaround you can create an applications and add objects which are in the package and run test on that application using the Start rule test application smart service. Creating applications for sprints /stories is a common practice in many projects. 

Alternatively, if you have test cases added into your expression rules then during compare and deploy of the package you can run the rules test cases in one click and verify failed rules in one screen itself. 

Unfortunately, Smart services only support testing at the application level or system level, not at the package level. There's no smart service that can test just a specific package or patch.
I would recommend you to go through below links for better approach.
https://docs.appian.com/suite/help/25.2/Running_Automated_Tests_on_Expression_Rules_with_Jenkins.html
https://docs.appian.com/suite/help/25.2/testing-applications.html

No way unfortunately. I would suggest you log a feature request with Appian Support to return unit test results when exporting a package via the API or the ability to run tests at the package level or even rule in the Smart Service.