Update BrainScaleS packages and py-torch

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!244

Until now we used a lot of try/except to keep going when preparing the
environment for the build; it should just work now, so let's fail early.

This should fix problems with finding system-installed headers instead of the
spack-provided ones (e.g. googletest). (In some cases sites might inject
include paths via compiler settings (or other means)).

We allow for newer py-pybind11 versions than upstream; upstream pins a specific
version, but, e.g., arbor needs a newer one. Currently, this should just work
fine :).

fix py-quantities installation issue (avoid building with setuptools)

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!251

Update quantities to 0.14.0

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!246

Add sda

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!247

Avoid LD_LIBRARY_PATH in pynn-brainscales&hxtorch

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!243

We encountered build fails on some HPC sites due to openssl mismatches
between bare-metal tools and spack — especially curl and similar tools
for fetching.
Our build tool, waf, needs to find spack-provided libraries, e.g.
libclang.so, at runtime… so we will only set the environment variable
for this.

Add NEST 3.4_rc1

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!234