[Feature] Create a Squeeze transform and update Unsqueeze transform

[reachsumit]

Description

Create a Squeeze transform and update Unsqueeze transform

Motivation and Context

This code change is targeted to address the issue#393. "Create a Squeeze transform from the Unsqueeze transform".
close #393

Types of changes

• [x ] New feature (non-breaking change which adds core functionality)

Changes made:

• Implemented an inverse operation for Unsqueeze that would squeeze the input.
• Implemented a Squeeze transform that would be the flipped version of the unsqueeze.
• Wrote 3 tests: 1 for the unsqueeze inverse operation, one for the squeeze forward, and one for the squeeze inverse.
• Applied appropriate spec transformations if action is in the keys_inv_in and for all the keys in input_spec.

No pre-commit or pytest issues.

Checklist

Go over all the following points, and put an x in all the boxes that apply.
If you are unsure about any of these, don't hesitate to ask. We are here to help!

• [x ] I have read the CONTRIBUTION guide (required)
• My change requires a change to the documentation.
• [ x] I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.

[vmoens]

LGTM
I changed the gym version to provisionally fix the CI, let's see if tests pass!
I'll give it a deeper look then and approve in case it works ok :)

[vmoens]

good catch 😅 damn copy paste!

[vmoens]

Nit: we could create the torch.Size here

[reachsumit]

Thank you for looking into this. 'torch.Size' object doesn't seem to support item deletion, which is conditionally required on line 481.