TRL ships unified GRPOConfig + on-policy distillation recipe — RLHF stack catches up to the SEED/LongStraw paper direction

Hugging Face TRL's docs document a unified GRPOConfig across the PPO/GRPO/DPO trainer families, a new on-policy distillation recipe aligned with the SEED/LongStraw paper direction, and improved LoRA support in the PPO trainer. The on-policy distillation recipe is a particularly important step for community reproductions — it lets a single open-weight policy act as both rollout actor and trajectory analyzer, refreshed each iteration, mirroring the SEED paper's self-evolving actor+analyzer pattern. The unified GRPOConfig simplifies the trainer switching cost that previously required separate config objects per algorithm.