Towards a from_abtem() function

[TomaSusi]

After the dev meeting, I got to vibe-coding with Claude to update abTEM to support the Zarr 3 ZipStore, which took some iterating due to metadata serialization.

In the end it looks like I managed to create a version that preserves compatibility with the old directory store, but if you save or load abTEM objects with .to_zarr("filename.zarr.zip") (or just .zip), it will use the ZipStore. This passes all tests, and also all objects I tried written to disk assert equal to those in memory.

I've pushed the changes to this pull request, could some of the quantem folks using abTEM verify that their workflows are still running?
abTEM/abTEM#247

[TomaSusi]

One design note: abTEM Measurement objects can have an arbitrary number of ensemble axes, and their order may vary depending on the specific calculation. Handling that gracefully will probably be the biggest issue for the implementation.

[TomaSusi]

We had a look with George in Vienna, and it looks like we can get all the necessary metadata with just a standard Zarr reader :)