Remove TorchTune service and related dev projects (#520)

* Remove TorchTune service and full-parameter fine-tuning support

Removes:
- src/art/torchtune/ directory (service, recipe, config, batch)
- src/art/dev/torchtune.py (TorchtuneArgs, TorchtuneModel types)
- examples/temporal_clue/temporal-clue-torchtune.ipynb
- dev/tau-bench/run_training.py, run.ipynb
- dev/swebench/train.ipynb

Updates:
- src/art/dev/__init__.py: Remove TorchtuneArgs export
- src/art/dev/model.py: Remove torchtune_args from InternalModelConfig
- src/art/dev/get_model_config.py: Remove torchtune logic
- src/art/local/backend.py: Remove TorchtuneService branching
- pyproject.toml: Remove torchtune dependency
- uv.lock: Updated to remove torchtune

The codebase now supports Unsloth (LoRA) and Tinker services only.
Megatron support will be added in the future.

* Remove dev/tau-bench and dev/swebench projects and sweagent dependency

These experimental projects are no longer actively maintained and can be
recovered from git history if needed.

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Co-authored-by: Cursor Bot <bot@cursor.com>

Author: corbt