VisibilityXds (and SpectrumXds): scan_number (int) => scan_name (str)

[FedeMPouzols]

Resolves #333.

---

Note well:

This contribution is made under the current ALMA software agreements. 
(c) European Southern Observatory, 2024, 2025
Copyright by ESO (in the framework of the ALMA collaboration)

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[FedeMPouzols]

Note that this will fail the tests with "preconverted" vis.zarr datasets. I cannot upload to the dropbox folder, but I prepared this zip:
Antennae_North.cal.lsrk.split.ms.zip
This also needs to be changed for the S3 test I think (that one seems to have a "v5" which I'm not sure if implies some difference).

[Jan-Willem]

@FedeMPouzols I also have some changes that will require a new Antennae_North.cal.lsrk.split. I will merge this branch into mine and generate the new Antennae_North.cal.lsrk.split.