refactor: mod tests, add user_infos

- Introduced helper functions `create_flat_schema` and `create_nested_schema` to streamline schema creation for tests.
- Updated `test_nested_struct_evolution` to improve clarity and structure, ensuring it verifies schema adaptation correctly.
- Enhanced assertions in schema mapping tests to provide clearer error messages and improve test reliability.
- Added detailed checks for field structures in `test_adapt_column_with_nested_struct`, ensuring all expected fields are present and correctly structured.
- Improved overall organization of test cases for better readability and maintainability.