chore: added header file to check if it fixes CI build issue

cpp/negentropy_wrapper.c

@@ -1,4 +1,5 @@
 #include <iostream>
+#include <unordered_map>
 
 #include "negentropy.h"
 #include "negentropy/storage/BTreeMem.h"
@@ -226,4 +227,4 @@ void free_result(result* r){
         free((void *) r->need_ids[i].data);
     }
     free((void *)r->need_ids);
-}
+}