Clean up dependencies related to ersilia test module

[DhanshreeA]

Thank you for taking your time to contribute to Ersilia, just a few checks before we proceed

• Have you followed the guidelines in our Contribution Guide
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Description
Marking Scikit Learn, and Scipy as optional because those are only required by the ersilia test module to make the basic ersilia install lightweight.