Allow `LitModular` to load from checkpoints with states of `Adversary`

[mzweilin]

What does this PR do?

• Unhide Adversary.perturber to make use of all features of pl.Trainer.
• Use Adversary._register_load_state_dict_pre_hook() to avoid resuming from perturbation in a checkpoint.

Type of change

Please check all relevant options.

• [x] Improvement (non-breaking)
• [ ] Bug fix (non-breaking)
• [ ] New feature (non-breaking)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Testing

Please describe the tests that you ran to verify your changes. Consider listing any relevant details of your test configuration.

• [x] pytest
• [x] python -m mart experiment=CIFAR10_CNN_Adv trainer=gpu trainer.precision=16 reports 70.08%

Before submitting

• [x] The title is self-explanatory and the description concisely explains the PR
• [x] My PR does only one thing, instead of bundling different changes together
• [ ] I list all the breaking changes introduced by this pull request
• [x] I have commented my code
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have run pre-commit hooks with pre-commit run -a command without errors

Did you have fun?

Make sure you had fun coding 🙃

[mzweilin]

Is it not possible to filter in adversary.py or does load_state_dict not recurse? Hardcoding input_adv_ is a bad idea...

Good idea! I can override Adversary._load_from_state_dict().