feat: add forking per-file processing in C version and enable parallel flag in Rust benchmark

Add fork() call in retoor_c/isspam.c main loop to spawn child process for each input file, allowing parallel analysis. Update bench.py to pass -p flag to Rust binary risspam for enabling parallel execution mode. Rebuild isspam binary to reflect the C source changes.

retoor_c/isspam.c

@@ -313,12 +313,14 @@ int main(int argc, char *argv[]) {
 
     if (argc > 1) {
         for (int i = 1; i < argc; i++) {
-       
+           pid_t  pid = fork();
+           if(!pid){
             printf("File: %s\n", argv[i]);
             
             analyze_file(argv[i]);
             printf("\n");
-            
+            return 0;
+           }
         }
 
         return 0;