[Minor] Adding retry to gradient test cases to avoid failure

[frankaging]

Description

Currently, the gradient test cases may fail intermittently due to torch equal tolerance issue. Adding retries to avoid this to keep main branch stable.

Merging unit test cases into a single file for utils.

Testing Done

./juice/scr/wuzhengx/pyvene/pyvene/models/interventions.py:421: UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor).
  mask_sigmoid = torch.sigmoid(self.mask / torch.tensor(self.temperature))
.........Removing testing dir ./test_output_dir_prefix-0037c3
Removing testing dir ./test_output_dir_prefix-ddd423
Removing testing dir ./test_output_dir_prefix-ffb32e
Removing testing dir ./test_output_dir_prefix-045942
Removing testing dir ./test_output_dir_prefix-a95c17

----------------------------------------------------------------------
Ran 18 tests in 5.667s

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

[aryamanarora]

@frankaging why not use torch.isclose()?

[frankaging]

@ZhengPeterWang Adding peter for further refactory