[BUGFIX] `argilla`: support read draft response models without values

This PR supports reading responses from the server in a draft status with no values in any of the questions (A clear form). This will be read as no responses in the new SDK (@burtenshaw we should validate this).

Closes https://github.com/argilla-io/argilla/issues/5049

Type of change

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

How Has This Been Tested

Checklist

I added relevant documentation
follows the style guidelines of this project
I did a self-review of my code
I made corresponding changes to the documentation
I confirm My changes generate no new warnings
I have added tests that prove my fix is effective or that my feature works
I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

argilla-io / argilla

[BUGFIX] `argilla`: support read draft response models without values #5124