Replace or Update Deprecated Zarr Notebooks and References

[chris-durbin]

There are two notebooks in the repository that reference deprecated Zarr libraries and services:

• external/zarr-eosdis-store.ipynb
• external/cof-zarr-reformat.ipynb

These notebooks should either be removed or updated to use VirtualiZarr instead, as it is the recommended alternative.

[chris-durbin]

FYI @asteiker and @owenlittlejohns