On single-CPU systems, skip tests which are known not to work

[sanvila]

Hello. While building this package on a single-CPU system I noticed that two tests fail.

test_cpu_affinity_neighbor_loader() fails in this way:

E ValueError: More workers (got 2) than available cores (got 1)

and test_multithreading_neighbor_loader() fails in this way:

E ValueError: 'worker_threads' should be smaller than the total available number of threads 1 (got 2)

I guess those tests are simply not suitable to be executed on single-CPU systems, so the proposed MR uses os.cpu_count() to test before executing them.

The failures may be reproduced easily by booting with GRUB_CMDLINE_LINUX="nr_cpus=1".

Thanks.

[sanvila]

Hello. On AWS instances of type c7i.large or m7i.large, having one core and 2 threads (2 vCPUs in total), this patch I proposed some time ago is not enough (still fails with the same error).

I've modified the patch to use psutil.cpu_count instead.

[sanvila]

Thank you. I'm also changing slightly the wording of the commit message to be in line with the wording of the code.

[akihironitta]

Thank you. I'm also changing slightly the wording of the commit message to be in line with the wording of the code.

All commits are squashed into one when merging the PR, so it doesn't matter much, but thank you!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.79%. Comparing base (c211214) to head (ae237ff).
⚠️ Report is 102 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9817      +/-   ##
==========================================
- Coverage   86.11%   85.79%   -0.32%     
==========================================
  Files         496      498       +2     
  Lines       33655    34132     +477     
==========================================
+ Hits        28981    29284     +303     
- Misses       4674     4848     +174     

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