Update to use sockets instead of numa_domains with pika's resource partitioner

[msimberg]

Fixes a breaking change introduced in pika 0.28.0.

I've taken the opportunity to fix a TODO that required a newer version of pika: check whether pika has been initialized before accessing the resource partitioner.

[msimberg]

cscs-ci run

[msimberg]

This will keep failing in CI for now because spack/spack#46062 is required to find Boost properly with pika 0.28.0. Once spack/spack#46207 is merged I'll update the spack commit here.

[msimberg]

Note that this breakage is another great reason to move the MPI pool initialization into pika with #1125.

[msimberg]

Once I update the spack commit, it might make sense to make some CI configurations use older, fixed, versions of pika. Any objections or wishes for which pipelines should have older versions if any?

[msimberg]

cscs-ci run

[msimberg]

cscs-ci run

[msimberg]

cscs-ci run

[msimberg]

cscs-ci run

[msimberg]

This is now ready for review. The disabled stdexec pipelines are tracked in #1184. The clang-based stdexec pipelines are still enabled, so we do still have some stdexec tests running even with the GCC ones disabled for now.