Feature379 ckksvector shape

[mrader1248]

Description

As stated in issue #379, it is strange that the property shape is defined for AbstractTensor, but calling it on a CKKSVector raises an error. Therefore, I have overriden the property shape for CKKSVector, simply calling the method size.

Affected Dependencies

None

How has this been tested?

• Added a unit test for shape almost identical to the one for size.

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the OpenMined Styleguide
• [ ] I have labeled this PR with the relevant Type labels
• [x] My changes are covered by tests

[bcebere]

Thank you for your contribution! LGTM!