make controller

src/Actions/DiffDaysAction.php

+<?php
+
+namespace App\Actions;
+
+use DateTimeImmutable;
+
+class DiffDaysAction
+{
+    /**
+     * Вернет кол-во дней между датами
+     * @param DateTimeImmutable $dateStart дата начала
+     * @param DateTimeImmutable $dateEnd дата окончания
+     * @return int
+     * */
+    public function act(
+        DateTimeImmutable $dateStart,
+        DateTimeImmutable $dateEnd
+    ): int {
+        return (int) $dateStart->diff($dateEnd)->format('%a');
+    }
+}