nanochat

delete autocast, an unnecessary thorn in my side, manage dtypes directly

Ensure that inputs and targets are contiguous (#569)

Document new Leaderboard entry congrats @ddudek for pointing out ClimbMix, time to GPT-2 is now 2.01 hours, down from 2.76 previously

big, breaking change but large upside: swap previous FineWeb-EDU dataset to NVIDIA ClimbMix dataset. Requires people to download the data shards. The upside is that training GPT-2 capablity model now only takes ~2 hours, down from 2.76 hours, so this is a huge win data-wise

document the legacy fineweb100b dataset and the new climbmix400b dataset