.plan-26-12: Zarr across space and TESSERA time (opens in new tab)

*2026-03-22 — note* I've been on leave this week so not much coding, but I did progress some threads from last week which I'll update on\! ## TESSERA+Zarr take 3 After I published the TESSERA Zarr conventions from last week, I got a load of useful feedback from other, more experienced Zarr heads. Issue \#1 convinced me to rearrange our layout fundamentally to include the embedding year as a dimension, and also to reduce the chunk size to make the shard/chunk coarser but still reasonably ...