add: Migrate vit gradcam code + pytorch export format for classificat…

[AlessandroPolidori]

Summary

Features:

• Gradcam for Visual Transformers in Classification and SklearnClassification tasks using Attention Gradient Rollout!
• Now Classification and SklearnClassification tasks can export models also in pytorch format
• This format is used by their respective evaluation/test tasks, so you can compute gradcams also when you test an already trained model. Other tasks currently export only in torchscript format and their respective eval. tasks can only import torchscript models.

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

Please confirm that the following tasks have been completed:

• I have tested my changes locally and they work as expected. (Please describe the tests you performed.)
• I have added unit tests for my changes, or updated existing tests if necessary.
• I have updated the documentation, if applicable.
• I have installed pre-commit and run locally for my code changes.

[lorenzomammana]

There are still some points I would review

[lorenzomammana]

Almost there 🔜

[lorenzomammana]

LGTM