feat: constraint validators

docs/pages/docs/features/validation/index.md

src/Constraint.php

src/Constraint/AnyConstraint.php

src/Constraint/AnyConstraintTest.php

src/Constraint/ConstConstraint.php

src/Constraint/ConstConstraintTest.php

src/Constraint/EnumConstraint.php

src/Constraint/EnumConstraintTest.php

src/Constraint/IntegerConstraint.php

src/Constraint/IntegerConstraintTest.php

src/Constraint/NumberConstraint.php

src/Constraint/NumberConstraintTest.php

src/Constraint/ObjectConstraint.php

src/Constraint/ObjectConstraintTest.php

src/Constraint/StringConstraint.php

src/Constraint/StringConstraintTest.php

src/Constraint/TupleConstraint.php

src/Constraint/TupleConstraintTest.php

src/ConstraintDefaultValue.php

src/ConstraintPath.php