Bug: Light Curves notebook lost access to ZTF data

[troyraen]

In the light_curve_generator.md notebook, the ztf_get_lightcurves function no longer works because it relies on DR18 which is no longer available through IRSA. To clarify: We put the actual ZTF DR18 Lightcurves files in an S3 bucket specifically for this purpose -- the call to IRSA's on-premise service was a necessary prerequisite to fetching the cloud data because of the way ZTF structures its Lightcurves dataset. IRSA only serves the 5 most recent ZTF DRs from on premise, so we lost access to DR18 when DR23 was released in Jan 2025.

Option 1:

Replace the DR18 files that are in the bucket with the same files for DR23. The notebook code should then only need a single line changed to point to the new DR and work again.

Option 2:

A HATS version of ZTF DR23 is currently in prep. Using this version would eliminate the need to call the on-premise service, which would be a good improvement for this notebook. It would require a refactoring of ztf_get_lightcurves, but this was always the intention for this function (#367).

[troyraen]

I think we are close enough to having the HATS version available in a Fornax-accessible bucket that my preference is to wait for it. But if there is a real need for this function to work again before the dataset and updated code are ready, then I can do option 1.