Dataset card: add mesh_1200_DES

Add 13-LPT-MassMapping/mesh_1200_DES (1200^3 DES Y3 MAP on 32 GPUs, 16 x 2 pencils)

Add dataset card

Copy files from datasets/ASKabalan/jax-fli-experiments

Add notebooks 16/17 field-level chains

Add notebook-14 MAP mass-mapping runs (416^3, DES Y3 and Euclid)

LFS rules for Orbax checkpoints

initial commit