797: Default range question type to start at 0

[Zachary-Sutherby]

Closes #797

Why is this the best possible solution? Were any other approaches considered?

Changed the default start to 0 instead of 1 based on the XLSForm specification: https://xlsform.org/en/#range

What are the regression risks?

Users / libraries expecting the default to be 1.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No change required for XLSForm docs, it appears ODK Docs doesn't specify range question defaults for start, end, and step.

Before submitting this PR, please make sure you have:

• included test cases for core behavior and edge cases in tests
• run python -m unittest and verified all tests pass
• run ruff format pyxform tests and ruff check pyxform tests to lint code
• verified that any code or assets from external sources are properly credited in comments