[Minor] Fix gradient backprop trainables with upstream interventions

[frankaging]

📝 Description

Currently, when using DAS with upstream interventions, gradient may throw arrow. This is due to some side-effect issues. We fix this by always-clone the passing activations in hook calls.

Testing Done

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Ran 49 tests in 43.641s

OK

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