Add a working DPO (Direct Preference Optimization) example using the
current Pydantic config schema with Llama 3.1 8B Instruct and QLoRA.
- examples/configs/dpo_example.yaml: DPO config with all core training
and LoRA parameters, plus commented-out advanced options
- examples/data/dpo_sample.jsonl: 8 preference pairs in DPO format
with ShareGPT-style message lists for chosen/rejected
- tests/test_dpo_example.py: 7 tests validating config loading, field
values, data format detection, and data validation
- examples/README.md: document the new DPO with QLoRA example