refactor: move static function on top of files

src/string.c

@@ -6,6 +6,8 @@
 #include "config.h"
 #include "string.h"
 
+static bool is_digit(char c) { return c >= '0' && c <= '9'; }
+
 unsigned int string_trim(char *str) {
   // https://www.delftstack.com/howto/c/trim-string-in-c/
   unsigned int start;
@@ -37,8 +39,6 @@ unsigned int string_trim(char *str) {
   return end - start + 1;
 }
 
-static bool is_digit(char c) { return c >= '0' && c <= '9'; }
-
 bool string_is_number(const char *value) {
   unsigned long value_len;