Do not write unused VDS files in the first place

[d-perl]

When, in artemis, we have a large grid, there are more than two datasets linked in the nexus files, and for the second nexus file, the first dataset may not be used. In that case,

https://github.com/DiamondLightSource/python-dlstbx/blob/main/src/dlstbx/swmr/h5check.py

fails when running

plist = dataset.id.get_create_plist()
...
vspace = plist.get_virtual_vspace(0)
frames = vspace.get_regular_hyperslab()[3][0]

because that dataset has no corresponding slab of the vds.

I would like it if completely unused datasets are not linked in the nexus file.

[d-perl]

Turns out the issue is not just that it is linked but that it is actually used as a source for the VDS as well

[DominicOram]

#92 fixes this issue and is good as an urgent fix required for the beamline but I think we could do more:

• This will strip any files out at the start of the datasets but not at the end (we currently do this inside Artemis itself but makes more sense to do in nexgen)
• Adding the files in then cleaning them up later is a bit messy, we can probably tidy it to never add them
• More tests around this would probably be good

[DominicOram]

This is still not fixed properly, and should be looked into