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.
• 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)