Resolve modernize-type-traits

[vil02]

This PR resolves modernize-type-traits and does some additional changes in that spirit (i.e. usage of _v for the CXXGraph-traits).

The formatting change comes from clang-format.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.02%. Comparing base (376d91b) to head (423453f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #549   +/-   ##
=======================================
  Coverage   97.02%   97.02%           
=======================================
  Files          97       97           
  Lines       11585    11585           
  Branches      768      768           
=======================================
  Hits        11240    11240           
  Misses        345      345           

Flag	Coverage Δ
unittests	97.02% <ø> (ø)

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