[P1] Gradent interventions tests

[ZhengPeterWang]

Description

Add trainable interventions tests with gradient flows

Testing Done

Test trainable interventions

Checklist:

• [x] My PR title strictly follows the format: [Your Priority] Your Title
• [x] I have attached the testing log above
• [x] I provide enough comments to my code
• [x] I have changed documentations
• [x] I have added tests for my changes