Handle overflow and underflow - checked

---

• checked_add
• Returns and Option that, is either the incremented value wrapped in Some or None.

examples/numbers/handle-overflow-checked-add/src/main.rs

fn main() {
    let mut num: i8 = 126;
    println!("{num}");

    num = num.checked_add(1).unwrap_or(42);
    println!("{num}");

    num = num.checked_add(1).unwrap_or(42);
    println!("{num}");
}

126
127
42