Generate random cache subdirectory for dataset job runner
Generate random cache subdirectory for dataset job runner.

This might fix the stale file handle error:
```
OSError: [Errno 116] Stale file handle
```

See: https://huggingface.co/datasets/tapaco/discussions/4
Generate random cache subdirectory for dataset job runner: Generate random cache subdirectory for dataset job runner.

This might fix the stale file handle error:
```
OSError: [Errno 116] Stale file handle
```

See: https://huggingface.co/datasets/tapaco/discussions/4