minor: Add templated types to flush_after (#719)

Author: BackEndTea

src/Persistence/PersistenceManager.php

@@ -76,7 +76,11 @@ public function save(object $object): object
     }
 
     /**
-     * @param callable():mixed $callback
+     * @template T
+     *
+     * @param callable():T $callback
+     *
+     * @return T
      */
     public function flushAfter(callable $callback): mixed
     {

src/Persistence/functions.php

@@ -149,7 +149,11 @@ function delete(object $object): object
 }
 
 /**
- * @param callable():mixed $callback
+ * @template T
+ *
+ * @param callable():T $callback
+ *
+ * @return T
  */
 function flush_after(callable $callback): mixed
 {