[Bug] cityscapes/singletask_learning_bench/semantic-segmentation: stale paths, train_url/test_url mismatch, and no README #1007

What happened:
Running the singletask_learning_bench/semantic-segmentation example as documented in benchmarkingjob.yaml fails immediately, due to three stacked issues:

1. Four hardcoded paths point to singletask_learning_bench/ instead of singletask_learning_bench/semantic-segmentation/:

   • benchmarkingjob.yaml (testenv: and algorithm url:)
   • testenv/testenv.yaml (map.py url:)
   • testalgorithms/rfnet/rfnet_algorithm.yaml (basemodel.py url:)
     These are stale, likely left over from before this example was nested under semantic-segmentation/.

2. testenv/testenv.yaml uses train_url/test_url, which core/testenvmanager/dataset/dataset.py's process_dataset() does not recognize (only train_index/train_data/train_data_info are handled), causing:
   NotImplementedError: not one of train_index/train_data/train_data_info
   Same bug class as [Bug] testenv.yaml uses train_url/test_url which are not recognized by ianvs core dataset processor in multiedge_inference_bench #604 (fixed in multiedge_inference_bench) and [Bug] robot-cityscapes-synthia/.../testenv.yaml uses train_url/test_url, not recognized by ianvs core dataset processor #1002 (open, robot-cityscapes-synthia) — this is a third occurrence.

3. There is no README anywhere in this example's folder, so there are no instructions for where to get the dataset the config expects at ./dataset/cityscapes/train_data.txt.

What you expected to happen:
The example should run end-to-end following its own config, or at minimum have a README explaining dataset setup, consistent with other examples in the repo.

How to reproduce it (as minimally and precisely as possible):
cd ianvs
ianvs -f examples/cityscapes/singletask_learning_bench/semantic-segmentation/benchmarkingjob.yaml

Fails first with:
RuntimeError: not found testenv config file(./examples/cityscapes/singletask_learning_bench/testenv/testenv.yaml) in local

After correcting the four stale paths, fails with:
NotImplementedError: not one of train_index/train_data/train_data_info

After renaming train_url/test_url to train_index/test_index, fails with:
ValueError: dataset file(./dataset/cityscapes/train_data.txt) is not a local file and not a absolute path.

Anything else we need to know?:
I have fixes ready for #1 and #2 (path corrections + key rename) and am happy to open a PR. For #3, I'd need guidance on where the cityscapes dataset for this example should be sourced from before I can write the README.