Upgrade CMAKE_CXX_STANDARD to 20

[scopreon]

Issue number of the reported bug or feature request: NAN

Describe your changes
Upgrade supported C++ version from 17 to 20

Testing performed
CI should pass

Additional context
Add any other context about your contribution here.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.19%. Comparing base (debc9e8) to head (d749a45).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #308   +/-   ##
=======================================
  Coverage   79.19%   79.19%           
=======================================
  Files          51       51           
  Lines        5542     5542           
  Branches      577      577           
=======================================
  Hits         4389     4389           
  Misses       1153     1153           

Flag	Coverage Δ
cpp	79.19% <ø> (ø)
python	79.19% <ø> (ø)

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[sarahmonod]

This looks good to me in principle, but I'm not sure why we were using C++17 to begin with, so I'd like Matt's input

[godlygeek]

I'm reasonably convinced that our CI would catch any problems with this. The fact that we were able to successfully produce manylinux_2_17 and musllinux_1_2 wheels means that this doesn't introduce any runtime dependencies on newer versions of libstdc++ or libc than we're able to depend upon, which would have been my only concern about upgrading.

So, I think this is safe... any objections, @pablogsal?

[pablogsal]

No concerns, we have done this with cpp17 in the past iirc with no problems as well

[sarahmonod]

LGTM, thanks @scopreon !