strparse: switch to curl_off_t as base data type

- add hex and octal parsers to the Curl_str_* family
- make curlx_strtoofft use these parsers
- remove all use of strtol() and strtoul() in library code
- generally use Curl_str_* more than strtoofft, for stricter parsing
- supports 64-bit universally, instead of 'long' which differs in size
  between platforms

Extended the unit test 1664 to verify hex and octal parsing.

Closes #16336

lib/ftplistparser.c

@@ -547,7 +547,7 @@ size_t Curl_ftp_parselist(char *buffer, size_t size, size_t nmemb,
           parser->item_length ++;
           if(c == ' ') {
             const char *p = &mem[parser->item_offset];
-            size_t hlinks;
+            curl_off_t hlinks;
             mem[parser->item_offset + parser->item_length - 1] = 0;
 
             if(!Curl_str_number(&p, &hlinks, LONG_MAX)) {