Upgrade nixpkgs to 23.11

[jacg]

This is blocked by meson not being able to find Geant4 after upgrading to 23.11. We haven't managed to get any insight into why this might be happening.

As a temporary hack, we tried using Geant4 from 23.05 and everything else from 23.11. As a knock-on effect this also forces us to use Qt from 23.05 and then things appear to work, but there are a few glitches, such as

• debug symbols disappearing from Geant4
• the client executable crashing at startup on MacOS

which may or may not be a consequences of mixing nixpkgs versions.

So we are sticking to 23.05 on master, for now. Eventually we'll have to upgrade. The python polars package is an example of something that we really want to take from 23.11 rather than 23.05.

[jacg]

Now that 24.05 is out, has this problem gone away ?

[gonzaponte]

I don't remember all the details about the 23.11 failure, but in 24.05 the problem is that cmake doesn't find some of the geant4 modules. This is odd, since omitting the modules : ... argument in the geant4 dependency call raises a warning that lists all the available modules, including the ones it doesn't find. Removing the missing modules from the list seems to work, or at least it compiles. It's unclear whether we will encounter other issues related to the missing modules in the future, but it's a start.

Two tests fail, both due to the change in Geant4 version:

• Finally, water is a liquid. We were testing for solid.
• We were using the Geant4 interface incorrectly, causing a segfault.

Both were easily corrected.

[jacg]

water is a liquid. We were testing for solid

That's because Geant4 used to think that water is solid at STP. This seems to have been fixed now.

[gonzaponte]

Yes, exactly.