Fix/test labels

[AlexGherardelli]

Description

• Fix data types accepted in get_choice_labels
• Add basic tests for the label.py helper functions
• Add synthetic data in CSV (test_survey.csv and test_xlsform.csv ) for further testing

Related Issue

Type of Change

• 📚 Examples / docs / tutorials / dependencies update
• 🔧 Bug fix (non-breaking change which fixes an issue)
• 🥂 Improvement (non-breaking change which improves an existing feature)
• 🚀 New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 🔐 Security fix

Checklist

• I've updated the code style using make codestyle.
• I've written tests for all new methods and classes that I created.
• I've written the docstring in Google format for all the methods and classes that I used.
• My commits follow the Conventional Commits format (fix:, feat:, chore:, etc.).