upgrade to php 8 code example

Example 1: php 8

latest version of php.
see new features at https://php.watch/versions/8.0

Example 2: php8

// php 8 Union type
class Number {
  public function __construct(
    private int|float $number
  ) {}
}

new Number('NaN'); // TypeError

Example 3: php8

// php8 class and construct
class Point {
  public function __construct(
    public float $x = 0.0,
    public float $y = 0.0,
    public float $z = 0.0,
  ) {}
}