Time-bounded investigation: use experimental branch of anemoi-datasets with zarr3 features

[tjhunter]

Anemoi-datasets does not currently support zarr3, see issue below. It has been worked on in the branch below but it has not been prioritized yet for compatibility issues.

The goal of this task is to report: can the weathergenerator depend on this special version of anemoi-datasets to:

• read the anemoi data such as era5 as before
• read radklim (or another dataset) with virtualizarr

The goal is investigative, not to implement a full reader. Bound it to a week's work max.

ecmwf/anemoi-datasets#220
ecmwf/anemoi-datasets#290