Implement PHP 8.3 features 🚀

[hemberger]

• Add types to all class constants.
• #[\Override] attribute for all intentionally overridden methods by child classes.
• Replace random_* with Randomizer::getBytesFromString()
  • For random_alphabetic_string, we can replace this with a random letter followed by (N-1) random letters/numbers and merge it into random_string. This will ensure that the string always has at least one letter in it and thus won't be implicitly converted to a number.
• Check if new DOMDocument methods can be leveraged.