Add date normalization and denormalization functionality

Introduce methods to normalize and denormalize DateTime objects using specific formats. Also, implement corresponding unit tests to ensure correct handling of single and multiple Doctrine entities, as well as date normalization.

src/Bundle/ChillMainBundle/Export/ExportDataNormalizerTrait.php

@@ -39,4 +39,30 @@ trait ExportDataNormalizerTrait
 
         return $object;
     }
+
+    public function normalizeDate(\DateTimeImmutable|\DateTime $date): string
+    {
+        return sprintf(
+            '%s,%s',
+            $date instanceof \DateTimeImmutable ? 'imm1' : 'mut1',
+            $date->format('d-m-Y-H:i:s.u e'),
+        );
+    }
+
+    public function denormalizeDate(string $date): \DateTimeImmutable|\DateTime
+    {
+        $format = 'd-m-Y-H:i:s.u e';
+
+        $denormalized = match (substr($date, 0, 4)) {
+            'imm1' => \DateTimeImmutable::createFromFormat($format, substr($date, 5)),
+            'mut1' => \DateTime::createFromFormat($format, substr($date, 5)),
+            default => throw new \UnexpectedValueException(sprintf('Unexpected format for the kind selector: %s', substr($date, 0, 4))),
+        };
+
+        if (false === $denormalized) {
+            throw new \UnexpectedValueException(sprintf('Unexpected date format: %s', substr($date, 5)));
+        }
+
+        return $denormalized;
+    }
 }