fixes nightlies due to UB errors; increase maxCPU hard limits

[ringabout]

ref #25217

The issues is actually that there is a hard limit for max cpus in niminst: #25219, which set to 20 while there is a 21 cpus now

[ringabout]

And we build nim c -d:danger -r tools/niminst/niminst, which allows -d:danger to live up to its name. We should probably change it to -d:release in the following PRs

[github-actions]

Thanks for your hard work on this PR!
The lines below are statistics of the Nim compiler built from c0fa868

Hint: mm: orc; opt: speed; options: -d:release
183144 lines; 8.288s; 661.699MiB peakmem