Fix: Strong types

[sandro-elsweijer]

Closes #1935

Describe your changes here:
I observed two minor things in our strong types.

1. the bool of is_reference has to be directly accessed by is_reference::value or is_reference_v.
2. The std::move in get is not evaluated because we return a reference and it would also cast away the const. It gets re-consted by the return value but thats a little sketchy.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.64%. Comparing base (8a48993) to head (1939610).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1933   +/-   ##
=======================================
  Coverage   75.64%   75.64%           
=======================================
  Files         103      103           
  Lines       18623    18623           
=======================================
  Hits        14087    14087           
  Misses       4536     4536           

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