Feat/rule attributes

[gwillz]

Some seriously magical stuff. Instead of defining rules in the rules() method, this instead puts the rules directly next to their respective property definitions.

Such as:

public MyModel
{
    /** @var string */
    #[Rule('required')]
    #[Rule('email')]
    public string $address;
}

Calling ->validate() or using the AttributesValidator class can then process these into a ValidationException or errors array.

This supports PHP 7 environments with the @rule doc tag.

Notes:

• Unsure about calling it a Rule - should it be ValidationRule or Validate ?