Refactor transaction handling for signature state changes, to wrap them into transactions

Wrap signature state changes in transactions to prevent race conditions and ensure data integrity. Update controller and test class names to reflect broader state change capabilities. Enhance documentation with comments to clarify transaction requirements and procedure details for signature operations.

src/Bundle/ChillMainBundle/Workflow/Messenger/PostSignatureStateChangeHandler.php

@@ -33,9 +33,12 @@ final readonly class PostSignatureStateChangeHandler implements MessageHandlerIn
             throw new UnrecoverableMessageHandlingException('signature not found');
         }
 
-        $this->signatureStepStateChanger->onPostMark($signature);
+        $this->entityManager->wrapInTransaction(function () use ($signature) {
+            $this->signatureStepStateChanger->onPostMark($signature);
+
+            $this->entityManager->flush();
+        });
 
-        $this->entityManager->flush();
         $this->entityManager->clear();
     }
 }