Refactor subject conversion APIs and simplify usage in audit-related components

- Removed `convertEntityToSubjects` method from `SubjectConverterManager` and updated all references to use `getSubjectsForEntity`.
- Ensured `getSubjectsForEntity` always returns an array by wrapping single `Subject` instances.
- Replaced manual type handling in converters with `array_push` and improved code clarity in `AuditEvent2Trail` and related tests.
- Updated and fixed tests for the modified subject conversion logic to maintain coverage.

src/Bundle/ChillMainBundle/Audit/SubjectConverterManagerInterface.php

@@ -14,12 +14,7 @@ namespace Chill\MainBundle\Audit;
 interface SubjectConverterManagerInterface
 {
     /**
-     * @return list<array>
+     * @return list<Subject>
      */
-    public function convertEntityToSubjects(mixed $subject): array;
-
-    /**
-     * @return Subject|list<Subject>
-     */
-    public function getSubjectsForEntity(mixed $subject): Subject|array;
+    public function getSubjectsForEntity(mixed $subject): array;
 }