Add Dedicated Constraint Attributes for JSON Schema Validation

[butschster]

This PR implements dedicated constraint attributes that work alongside the existing Field attribute to provide modular, composable JSON Schema validation. Instead of bloating the Field attribute with validation concerns, this creates focused, single-purpose attributes that can be combined for powerful validation rules.

🚀 Features

New Constraint Attributes

• #[Pattern(regex)] - String pattern validation with regex
• #[Length(min, max)] - String/array length constraints
• #[Range(min, max, exclusiveMin, exclusiveMax)] - Numeric range validation
• #[MultipleOf(value)] - Numeric multiple validation
• #[Items(min, max, unique)] - Array item constraints
• #[Enum(values)] - Enumeration validation

💡 Usage Examples

Basic Constraints

final class User
{
    public function __construct(
        #[Field(title: 'Full Name')]
        #[Pattern('^[A-Z][a-z]+(?: [A-Z][a-z]+)*$')]
        #[Length(min: 2, max: 100)]
        public string $name,

        #[Field(title: 'Age')]
        #[Range(min: 13, max: 120)]
        public int $age,

        #[Field(title: 'Price')]
        #[Range(min: 0.01, max: 99999.99)]
        #[MultipleOf(0.01)]
        public float $price,
    ) {}
}

Array and Enum Constraints

final class Post
{
    public function __construct(
        #[Field(title: 'Tags')]
        #[Items(min: 1, max: 10, unique: true)]
        public array $tags,

        #[Field(title: 'Status')]
        #[Enum(['draft', 'published', 'archived'])]
        public string $status,
    ) {}
}

Mixed with PHPDoc Constraints

final class Product
{
    public function __construct(
        /** @var positive-int */ // PHPDoc constraint
        #[Range(max: 1000)] // Attribute constraint
        public int $quantity, // Results in: minimum: 1, maximum: 1000
    ) {}
}

📊 Generated JSON Schema

The above examples generate clean, standards-compliant JSON Schema:

{
  "type": "object",
  "properties": {
    "name": {
      "title": "Full Name",
      "type": "string",
      "pattern": "^[A-Z][a-z]+(?: [A-Z][a-z]+)*$",
      "minLength": 2,
      "maxLength": 100
    },
    "tags": {
      "title": "Tags", 
      "type": "array",
      "minItems": 1,
      "maxItems": 10,
      "uniqueItems": true
    },
    "status": {
      "title": "Status",
      "type": "string",
      "enum": ["draft", "published", "archived"]
    }
  },
  "required": ["name", "tags", "status"]
}