Fix super3 data prep rl subgroup bootstrap

[fallintoplace]

Summary

• register super3 data prep rl as a Typer subgroup instead of importing the shadowed prep.rl module surface
• remove the obsolete src/nemotron/cli/commands/super3/data/prep/rl.py dispatcher and add explicit rlvr, swe1, swe2, and rlhf data-prep command modules under the rl/ package
• add a CLI regression test and update the Super3 docs/comments that still advertised the flat super3 data prep rl entrypoint

Root cause

src/nemotron/cli/commands/super3/data/prep/_typer_group.py imported META and rl from nemotron.cli.commands.super3.data.prep.rl, but that path now has both a sibling rl.py file and an rl/ package. Python resolves the package first, and the package only exported rl_app, so the Super3 data-prep CLI broke during import/bootstrap.

Impact

After this change, super3 data prep rl loads as the intended subgroup and exposes all documented stage-specific subcommands:

• rlvr
• swe1
• swe2
• rlhf

Validation

• python3 -m compileall src/nemotron/cli/commands/super3/data/prep tests/recipes/super3/test_cli.py
• uv run --no-project --with pytest --with "nemo-run @ git+https://github.com/NVIDIA-NeMo/Run.git@main" --with typer --with rich --with textual --with fsspec --with numpy --with pyarrow --with xxhash --with "transformers>=4.57.6,<5.0" --with "huggingface_hub>=0.20.0" --with "datasets>=2.14.0" --with pyyaml --with tomlkit --with colorama --with "wandb>=0.23.1" --with jinja2 --with pydantic --with "pydantic-settings>=2.12.0" --with omegaconf env PYTHONPATH=src pytest tests/recipes/super3/test_cli.py

[chrisalexiuk-nvidia]

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