transformers safetensors qwen2 text-generation trl generated_from_trainer xpo conversational dataset:trl-lib/ultrafeedback-prompt arxiv:2405.21046 arxiv:2404.04656 base_model:Qwen/Qwen2-0.5B-Instruct base_model:finetune:Qwen/Qwen2-0.5B-Instruct autotrain_compatible text-generation-inference endpoints_compatible region:us