fix: Out-Of-Bounds bug in Unsqueeze

[gs-olive]

Description

• Implement support for negative-indexing in unsqueeze, in accordance with the torch.unsqueeze function
• Fix bug for TFT model in PyTorch, which requires negative indexing in unsqueeze
• Update core utility logic and comments

Desired Behavior:

torch.unsqueeze(torch.ones(4, 4), -1).shape
>>> (4, 4, 1)

torch.unsqueeze(torch.ones(4, 4), -3).shape
>>> (1, 4, 4)

Fixes #1779

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [ x ] My code follows the style guidelines of this project (You can use the linters)
• [ x ] I have performed a self-review of my own code
• [ x ] I have commented my code, particularly in hard-to-understand areas and hacks
• [ x ] I have made corresponding changes to the documentation
• [ x ] I have added tests to verify my fix or my feature
• [ x ] New and existing unit tests pass locally with my changes
• [ x ] I have added the relevant labels to my PR in so that relevant reviewers are notified

[narendasan]

LGTM