Update anemoi to support earthkit 1.0

[aaron-hopkinson]

Earthkit 1.0 is currently scheduled to be released over the coming months, and may have changes to the public APIs which require changes to anemoi (across the ecosystem, i.e. anemoi-datasets, anemoi-transform and anemoi-inference).

This issue covers the work required to update anemoi to support earthkit 1.0.
(Created in this repo since the changes are likely to be biggest in anemoi-datasets)

Example:

• ekd.from_source may return a new intermediate object, and anemoi-dataset Sources will need to be updated to use these new objects.