refactor FileSizeUnit enum

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

system/Files/FileSizeUnit.php

@@ -13,23 +13,30 @@
 
 namespace CodeIgniter\Files;
 
+use InvalidArgumentException;
+
 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"
+     *
+     * @throws InvalidArgumentException
+     */
     public static function fromString(string $unit): self
     {
         return match (strtolower($unit)) {
-            'b'  => self::B,
-            'kb' => self::KB,
-            'mb' => self::MB,
-            'gb' => self::GB,
-            'tb' => self::TB,
-            default => throw new InvalidArgumentException("Invalid unit: $unit"),
+            'b'     => self::B,
+            'kb'    => self::KB,
+            'mb'    => self::MB,
+            'gb'    => self::GB,
+            'tb'    => self::TB,
+            default => throw new InvalidArgumentException("Invalid unit: {$unit}"),
         };
     }
+
+    case B  = 0;
+    case KB = 1;
+    case MB = 2;
+    case GB = 3;
+    case TB = 4;
 }