Trim train_gpt_mlx_kl.py to ≤1500 lines; fix orphaned clip_grad_tree#8

kailean merged 2 commits intocopilot/create-clean-submission-ready-prkailean/parameter-golf:copilot/create-clean-submission-ready-prfrom

copilot/verify-aub-1-0-bpb-code-lengthkailean/parameter-golf:copilot/verify-aub-1-0-bpb-code-lengthCopy head branch name to clipboard