Add a memory-efficient chunked LM-head log-probability utility to trl/trainer/utils.py and export it from…

Add a memory-efficient chunked LM-head log-probability utility to trl/trainer/utils.py and export it from…: a task in HF ML Tasksmith (Harbor dataset). ChunkedLogProbFunction — a torch.autograd.Function that computes per-token log-probabilities and entropy without ever materializing the full N, V…