feat(convert/atou): adding the atou function

- Can be usefull when the parsing of some project (like philosophers)

includes/convert.h

@@ -6,13 +6,15 @@
 /*   By: rparodi <rparodi@student.42.fr>            +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2024/10/31 14:57:24 by rparodi           #+#    #+#             */
-/*   Updated: 2025/09/05 16:07:54 by rparodi          ###   ########.fr       */
+/*   Updated: 2025/09/08 10:17:01 by rparodi          ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
 #ifndef CONVERT_H
 # define CONVERT_H
 
+# include <stddef.h>
+
 /**
  * @brief Converts integer to string
  *
@@ -29,6 +31,14 @@ char			*ft_itoa(int n);
  */
 int				ft_atoi(const char *nptr);
 
+/**
+ * @brief Converts string to size_t
+ *
+ * @param nptr the string that will be converted
+ * @return The unsigned long long on the string
+ */
+size_t	ft_atou(const char *nptr);
+
 /**
  * @brief Converts string to long long integer
  *