In many programs, validating user input is a common and crucial task. Ensuring that input data adheres to expected formats and constraints can prevent bugs, enhance security, and improve user experience. In this challenge, you will create a function that validates a user's age and email, returning early if any conditions are not met.

Your task is to implement a function validate_user(age: i32, email: &str) -> Result<(), String> that validates the user's age and email. The function should follow these rules:

1. If the age is less than 0 or greater than 120, return an error with the message "Invalid age".
2. If the email does not contain an '@' symbol, return an error with the message "Invalid email".
3. If both the age and email are valid, return Ok(()).

Here's an example of how to use the early return technique:

fn early_return(name: &str, age: i32) -> Result<(), String> {
    if name.is_empty() {
        return Err("Name is empty".to_string());
    }
 
    if age < 0 {
        return Err("Invalid age".to_string());
    }
 
    Ok(())
}

let result = validate_user(25, "user@example.com");
assert_eq!(result, Ok(()));
 
let result = validate_user(-1, "user@example.com");
assert_eq!(result, Err("Invalid age".to_string()));
 
let result = validate_user(25, "userexample.com");
assert_eq!(result, Err("Invalid email".to_string()));

• Use the return keyword to exit the function early when an invalid condition is encountered.
• Consider using the contains method to check if the email contains an '@' symbol.