test(delete): differential + timing regression tests for per-directory delete plans

- Compare --delete-during/--delete-delay final state against rsync 3.4.1.
- Force a mid-transfer failure through a byte-slicing proxy: --delete-during has
  removed the processed directory's extra, --delete-delay has not.
- Create a destination entry while the transfer is in flight: it survives
  --delete-delay's snapshot but is removed by --delete-after's fresh end scan.
- Cover the --delete-delay type-conflict case now matching rsync.

src/client/client_send.c

@@ -1189,7 +1189,8 @@ static int send_chunk_delete_plans(Client* client, DeletePlanSender* plans, cons
     File* f = chunk->items[i];
     if (!f)
       continue;
-    if (delete_plan_send_for_path(client->file_descriptor, plans, file_wire_path(f), f->is_dir) != 0)
+    if (delete_plan_send_for_path(client->file_descriptor, plans, file_wire_path(f), f->is_dir) !=
+        0)
       return -1;
   }
   return 0;