Add StructuredMeshView as proxy between solver and actual StructuredMesh

[sloede]

Added a new mesh type called StructuredMeshView. Rather than defining a new mesh they provide a view on a given parent mesh. They provide an extended set of functionalities compared to ordinary meshes and can be used in the same way. Their main application is in coupled simulations.

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 96.09%. Comparing base (ff3106c) to head (169dd1c).

Files	Patch %	Lines
src/meshes/structured_mesh_view.jl	91.30%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1624      +/-   ##
==========================================
- Coverage   96.10%   96.09%   -0.01%     
==========================================
  Files         451      453       +2     
  Lines       36414    36461      +47     
==========================================
+ Hits        34993    35036      +43     
- Misses       1421     1425       +4     

Flag	Coverage Δ
unittests	96.09% <92.86%> (-0.01%)	⬇️

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[sloede]

A few final comments and suggestions, then this is good to merge imho. Thanks for pushing this forward!

[sloede]

LGTM!

[sloede]

@SimonCan LGTM! Can you do a review and approve this? It should then auto-merge once all tests have passed

[sloede]

Codecov hiccups 😢