Add unique constraint for PersonIdentifier, implement UniqueIdentifierConstraint with validation logic, and include supporting tests

- Introduce `UniqueIdentifierConstraint` and its validator for ensuring identifier uniqueness.
- Add a database-level unique constraint on `PersonIdentifier` (`definition_id`, `value`).
- Implement repository method to fetch identifiers by definition and value.
- Include integration and unit tests for validation and repository functionality.
- Update `Person` entity with `Assert\Valid` annotation for `identifiers`.

src/Bundle/ChillPersonBundle/Entity/Identifier/PersonIdentifier.php

@@ -12,10 +12,13 @@ declare(strict_types=1);
 namespace Chill\PersonBundle\Entity\Identifier;
 
 use Chill\PersonBundle\Entity\Person;
+use Chill\PersonBundle\PersonIdentifier\Validator\UniqueIdentifierConstraint;
 use Doctrine\ORM\Mapping as ORM;
 
 #[ORM\Entity]
 #[ORM\Table(name: 'chill_person_identifier')]
+#[ORM\UniqueConstraint(name: 'chill_person_identifier_unique', columns: ['definition_id', 'value'])]
+#[UniqueIdentifierConstraint]
 class PersonIdentifier
 {
     #[ORM\Id]