Refactor recipe validation and improve graph generation

The 'recipes.py' module is renamed to 'validation.py' and the 'RecipeValidation' class is renamed to 'Validation'. The code is refactored to use f-strings for better readability. Graph generation has also been improved by simplifying the way edges are added and returning information as a dictionary. An unnecessary png file generation has been removed. Changes have been made where these classes are imported and used.