refactor: add declare strict_types to all classes in ./src

[DannyvdSluijs]

This pull request includes significant changes to the project configuration and codebase to improve code quality and enforce strict typing. The main changes involve removing the PHP CS Fixer configuration file and adding strict type declarations to various files.

Configuration changes:

• Removed the PHP CS Fixer configuration file .php-cs-fixer.dist.php to streamline project setup and maintenance.

Code quality improvements:

• Added declare(strict_types=1); to enforce strict typing in multiple files across the src/JsonSchema/Constraints directory, including BaseConstraint.php, CollectionConstraint.php, ConstConstraint.php, Constraint.php, ConstraintInterface.php, EnumConstraint.php, Factory.php, FormatConstraint.php, NumberConstraint.php, ObjectConstraint.php, SchemaConstraint.php, StringConstraint.php, TypeCheck/LooseTypeCheck.php, TypeCheck/StrictTypeCheck.php, TypeCheck/TypeCheckInterface.php, TypeConstraint.php, and UndefinedConstraint.php. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
• Added declare(strict_types=1); to enforce strict typing in src/JsonSchema/ConstraintError.php and src/JsonSchema/Entity/JsonPointer.php. [1] [2]