feat: add benchmark target to Makefile and optimize isspam.c with stricmp

- Add 'benchmark' target to Makefile that extracts books archive and runs bench.py
- Reorder includes in isspam.c (rstr.h before rstring_list.h)
- Replace file_exists() with case-insensitive stricmp() for forbidden word matching
- Remove unused flags (show_capitalized, show_sentences, etc.) and stripws() function
- Add memory usage comment and fix trailing newline in rstr.h header guard

retoor_c/rstr.h

@@ -26,8 +26,6 @@ void stra(str_t *str, const char *to_append) {
     if (required_new_length > str->size) {
         str->size += required_new_length + str->buffer_size;
         str->content = (char *)realloc(str->content, str->size + 1);
-    } else {
-        // printf("NO NDEED\n");
     }
     strcat(str->content, to_append);
     str->content[str->length] = 0;
@@ -49,4 +47,4 @@ char *strc(str_t *str) {
     return content;
 }
 
-#endif
+#endif