Release: prepare for first CRAN release

[martinctc]

Summary

This PR prepares the surveytoolbox package for its first CRAN release.

This PR introduces a robust test suite for the surveytoolbox package using testthat, significantly improving code reliability and maintainability.

Changes

🔧 Functions Tested

Comprehensive test coverage for core package functions including:

• any_x - Enhanced any() function with NA handling
• as_percent - Number to percentage conversion
• box_it - Binary variable creation with labels
• CAGR - Compound annual growth rate calculations
• clean_strings - Variable name cleaning
• apply_row - Rowwise operations
• look_up - Lookup table functionality
• wrap_text - Text wrapping for visualizations
• Label functions (set_varl, set_vall)
• NPS functions (as_nps)
• Utility functions (maxmin, create_named_list, likert_convert)

Checks

• All R CMD checks pass
• roxygen2::roxygenise() has been run prior to merging to ensure that .Rd and NAMESPACE files are up to date.
• NEWS.md has been updated.

Change Type

Please check the type of change your PR introduces:

• Bugfix
• Feature (incl. changes to visualizations)
• Technical design
• Build related changes (e.g. tests)
• Refactoring (no functional changes, no api changes)
• Code style update (formatting, renaming) or Documentation content changes
• Other (please describe):

Notes

This fixes #<issue_number>

<other things, such as how to incorporate new changes>