docs(str): moving the actual documentation on the header

- The documentation on the header allow u to see on the files where the
header is inclued

str/ft_strlen.c

@@ -6,19 +6,12 @@
 /*   By: rparodi <marvin@42.fr>                     +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2023/11/07 16:56:24 by rparodi           #+#    #+#             */
-/*   Updated: 2025/09/01 18:34:21 by rparodi          ###   ########.fr       */
+/*   Updated: 2025/09/05 16:17:50 by rparodi          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
 #include <unistd.h>
 
-/**
- * @brief Computes the length of a string.
- * 
- * @param s The input string.
- * 
- * @return The number of characters in the string `s`.
- */
 size_t	ft_strlen(const char *s)
 {
 	size_t	i;