[lenaploetzke]

Closes #2590

Describe your changes here:
@sandro-elsweijer asked me why i return unique_ptrs in the constructor wrappers. While thinking about this, i noticed that we should not move or copy the mesh in general as we store pointers to the mesh in each element which we would have to update. copying or moving can also be a problem in between set_adapt and commit because of the desing of the adapt registry where we also store a ref to the mesh.
Therefore i decided to delete the (automatically constructed bc of the explicit destructor) copy and move constructor.

For the constructor wrappers:
It would still be possible to return the instance of the mesh and not the unique ptr because we keep the address there.
But with unique ptr, we keep the object copyable and moveable.
We would not be able to copy the mesh into an existing variable with the "by value return", e.g replacing a mesh with a new one or construting the mesh in another function and returning it by value (move needed).
With the unique ptr, such things are possible.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.05%. Comparing base (a2f03ec) to head (552a93e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2586   +/-   ##
=======================================
  Coverage   83.05%   83.05%           
=======================================
  Files         148      148           
  Lines       22259    22259           
=======================================
  Hits        18488    18488           
  Misses       3771     3771           

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