Support for zarr v3

[VeckoTheGecko]

Zarr v3 was released yesterday, causing our unit tests to fail.

See migration guide.

[VeckoTheGecko]

@erikvansebille In the implementation of this, should we completely drop support for Zarr v2? We could also provide support for both, but I'm not sure how useful that is (xarray supports zarr 2 and 3, and I don't know what other packages we can expect users to have in their environment that need zarr). What do you think? If keeping both is difficult, I think we should opt for dropping v2

[erikvansebille]

Hi @VeckoTheGecko, I think we can choose to only support zarr v3. Parcels is research software, we can expect users to use the latest packages in their environment. I propose in general to try reduce maintenance burden as much as possible by dropping support for older package versions