Restore Resize(scale=...) backward compatibility

- Add 'scale' as an optional parameter in Resize.__init__ that aliases to 'img_scale'
- Add 'scale' property with getter/setter for attribute-based access
- Update validation to handle placeholder values (int/float) used by RandomChoiceResize and RandomResize
- Update docstring to document 'scale' parameter for backward compatibility

This fixes TypeError in RandomChoiceResize and RandomResize which construct Resize with scale parameter. Maintains full backward compatibility while supporting the new img_scale API.

Author: GeorgePearse