Port to Ubuntu 26.04

[MakisH]

This PR bumps the Ubuntu version to 26.04 (based on the bento/ubuntu-26.04 box, first released yesterday) and enables the previously disabled components ASTE and Rust bindings (see #94).

It also changes the default number of cores to 4 and the RAM to 4GB.

Interesting in this release is that the FEniCS PPA is not needed anymore: there are now both FEniCS legacy and FEniCSx packages on Ubuntu Universe.

Notes:

• Since I am building custom Debian packages (to set the production-audit preset), and Switch the Debian package libxml2 dependency to libxml2-dev precice#2560 has not yet been released, I am applying the patch on top of main, to be able to say that the next distribution includes v3.4.1.
• SU2 needed a couple more patches for Ubuntu 26.04:
  • Ninja replaced the now deleted pipes library with shlex in ninja-build/ninja@9cf13cd
  • To be able to patch the Ninja submodule, I replaced getting the archive with cloning the SU2 repository and its submodules.
  • I could not build CGNS, but it does not seem to be needed, so I disabled it, as well as TECIO.
• I disabled the pre-fetching of the heat-exchanger meshes, since this step is now integrated into the run.sh (see Migrate heat-exchanger/download-meshes.sh into the run.sh scripts tutorials#805). This also saves a bit of space.

So far, I can confirm that the complete box builds. Proceeding with testing.

Issues:

• Paraview has no icons on its buttons. (I also documented it on the Kitware GitLab, and reported it on the Ubuntu Bugzilla). -> Was missing the qt6-svg-plugins package.
• There is no "extract" option for tar.gz files in the context menu of the file manager. -> was missing the thunar-archive-plugin package.
• While trying to install fenicsprecice, it builds scipy from source, which takes a while. I could re-introduce the central venv. Some people suggest upgrading PIP first.
• Similar to Ubuntu 24.04, Desktop shortcuts require being set as trusted. See some discussion. In any case, I could manually pre-set the launchers to trusted via the GUI, or restore a backup in subsequent builds. -> We anyway cannot have unattended builds anymore, and the manual set is trivial.
• Not sure if this is new, but there is a Failed to start vboxadd-service.service message at boot, followed by a Job systemd-networkd-wait-online.service/start running that times out after ~2min.
• There is a similar one about GRUB (see screenshot)

[MakisH]

I have tested all components, generally everything works.

Open issues:

• ParaView seems to have an issue where surface plots of cell data do not work, but there are sufficient workarounds. Documented in ParaView does not render surface plots of cell data #110.
• ccx2paraview seems to be incompatible with recent vtk versions: Incompatibility with vtk >= 9.4.0 calculix/ccx2paraview#58 While it is reported to work with 9.3.1, that is not supported by Python 3.14. I removed it for now.
• The FEniCS and FEniCSx adapters need bugfix releases to include Remove restrictions of the scipy version fenics-adapter#211 and Remove restrictions of the scipy version fenicsx-adapter#85. These adapters are installed at runtime in a virtual environment by each tutorial.

Edit: While I checked some DUNE and DUNE-FEM cases, I did not check DuMux. That might be broken.