feat: u256 exponentiation math function about kakarot-ssj HOT 1 CLOSED

// Raise a number to a power.
/// * `base` - The number to raise.
/// * `exp` - The exponent.
/// # Returns
/// * `felt252` - The result of base raised to the power of exp.
fn pow_u256(base: felt252, exp: felt252) -> felt252 {
    if exp == 0 {
        return 1;
    } else {
        return base * pow_u256(base, exp - 1);
    }
}

fn fast_pow(mut base: u256, exponent: u256) -> u256 {
    let mut result = 1;
    let mut exp = exponent;
    loop {
        if exp == 0 {
            break;
        };
        if (exp % 2) == 1 {
            result *= base;
        }
        base *= base;
        exp /= 2;
    };
    result
}