docs: improve file.inc documentation and remove stray braces

Add comprehensive documentation to the file header explaining the purpose
of helper functions and their safety checks. Remove trailing stray braces
that appear to be leftover code.

Author: jordikroon

include/file.inc

@@ -1,7 +1,9 @@
 <?php
 
 /*
- *
+ * This file contains helper functions to deal with files in a safe manner.
+ * These functions check for file existence and readability before performing
+ * any operations on them.
 */
 
 function file_get_size(string $filename): int|false
@@ -30,6 +32,3 @@ function file_get_contents_if_exists(string $filename): string|false
 
     return file_get_contents($filename);
 }
-{
-
-}