Now that we know about vectors and hashmaps, let’s tackle something more challenging. In this exercise, we’ll build a system to manage and analyze student grades. This challenge will help you practice working with structs, hashmaps, vectors, and methods while managing a collection of data.

The focus here is on functionality. Ignore error handling for this challenge; assume the input is always valid.

You need to define the StudentGrades struct, which contains a HashMap of student names (String) as keys and Student structs as values. Each Student struct should have the following fields:

• name: The name of the student (String).
• grades: A Vec<u8> to store the student's grades.

Implement the following methods for the StudentGrades struct:

1. add_student(name: &str): Add a new student to the HashMap. If the student already exists, do nothing.
2. add_grade(name: &str, grade: u8): Add a grade to an existing student.
3. get_grades(name: &str) -> &[u8]: Retrieve the grades of a student as an immutable reference.
4. Since there’s no error handling, assume all inputs are valid, and keys will exist when accessed.