curlftpfs: implement readdir

i think now all the stuff you'd expect of a basic fs now actually works

pkgs/additional/curlftpfs-sane/default.nix

@@ -17,7 +17,7 @@
     owner = "colin";
     repo = "curlftpfs";
     rev = "fuse3";
-    hash = "sha256-Vad9BSJCPllotk0t3IoJxlaUcmdoIdOIgXkZrNIHowE=";
+    hash = "sha256-bP8G1gzXaAnjpjVJQk4x1FHOlDqYWU9ZaAV5fEvTF14=";
   };
   # `mount` clears PATH before calling the mount helper (see util-linux/lib/env.c),
   # so the traditional /etc/fstab approach of fstype=fuse and device = curlftpfs#URI doesn't work.