Implement unit tests for CV data science code

[jfomhover]

PR into Azure/mlops-v2

Checklist

I have:

• read and followed the contributing guidelines

Changes

• added a tests/ directory under cv/data-science/src/ to unit test ds code
• implement unit tests for loading all models and for testing training end to end on a super small random dataset
• these unit tests should provide coverage of approx 90%

[cindyweng]

will merge and then test using main-jul31 to make sure it works