refactor FileSizeUnit enum

* reorder cases and function
* add DocBlock for return and throws

system/Files/FileSizeUnit.php

@@ -15,12 +15,13 @@
 
 enum FileSizeUnit: int
 {
-    case B  = 0;
-    case KB = 1;
-    case MB = 2;
-    case GB = 3;
-    case TB = 4;
-
+    /**
+     * Allows the creation of a FileSizeUnit from Strings like "kb" or "mb"
+     *
+     * @return FileSizeUnit
+     *
+     * @throws \InvalidArgumentException
+     */
     public static function fromString(string $unit): self
     {
         return match (strtolower($unit)) {
@@ -29,7 +30,13 @@ public static function fromString(string $unit): self
             'mb' => self::MB,
             'gb' => self::GB,
             'tb' => self::TB,
-            default => throw new InvalidArgumentException("Invalid unit: $unit"),
+            default => throw new \InvalidArgumentException("Invalid unit: $unit"),
         };
     }
+
+    case B  = 0;
+    case KB = 1;
+    case MB = 2;
+    case GB = 3;
+    case TB = 4;
 }