Add entities to grade class and make some improvements in the class

Required Actions

• Add JPA annotations to the Grade class to properly map it as a database entity.
• Add setters for Grade class fields.
• Improve the setScore method to restrict score values to a valid range between 0 and 100. If the score is outside this range, throw an IllegalArgumentException.
• Ensure proper validation for the grade assignment process in the class.

Expected Deliverables

• The Grade class should be updated with the required JPA annotations to make it a valid entity.
• Setters for the Grade class should be added to ensure proper data encapsulation.
• The setScore method should enforce that scores are only allowed between 0 and 100, with appropriate exception handling for invalid values.