Use local recorded dataset if exists

[xuaner233]

What this does

Explain what this PR does. Feel free to tag your PR with the appropriate label(s).

Use local lerobot dataset if it exists.

Case happened when we recorded dataset with --push-to-hub 0 --local-files-only 1 and then want to train with it, without this change, there could be exception like:

huggingface_hub.errors.RepositoryNotFoundError: 401 Client Error. (Request ID: Root=1-67726fa1-235cf0064b60bb1e645fb4cf;f9c85308-8970-46a9-bfbb-5a760a981530)

which is caused by default local_files_only=False in class LeRobotDataset .

Examples:

Title	Label
Enhance	Use existing local recorded dataset if exist

How it was tested

Explain/show how you tested your changes.

• No current tests breaking

How to checkout & try? (for the reviewer)

Provide a simple way for the reviewer to try out your changes.

Examples with SO100:

1. Record dataset

python lerobot/scripts/control_robot.py record \
  --robot-path lerobot/configs/robot/so100.yaml \
  --single-task "SO100 pick and place" \
  --fps 30 \
  --repo-id xuaner233/so100_pick_and_place \
  --tags "so100 pick" \
  --warmup-time-s 5 \
  --episode-time-s 30 \
  --reset-time-s 10 \
  --num-episodes 2 \
  --push-to-hub 0 \
  --local-files-only 1

2. Then trying to train with just recorded dataset:

python lerobot/scripts/train.py \
    dataset_repo_id=xuaner233/so100_pick_and_place \
    policy=act_so100_real \
    env=so100_real \
    hydra.run.dir=outputs/train/act_so100_pick_and_place \
    hydra.job.name=act_so100_pick_and_place \
    device=cuda

[xuaner233]

Thanks in advance for review!
Possible reviewers: @jess-moss @Cadene @aliberts