WIP: Sc/mhd treemesh 2d

[SimonCan]

This branch is a fork of the ns-treemesh-3d branch. It implements the compressible visco-resistive MHD equations in 2 dimensions on the treemesh.

Convergence test for examples/tree_3d_dgsem/elixir_mhd_diffusive_alfven_wave.jl:

####################################################################################################
l2
rho                 rho_v1              rho_v2              rho_v3              rho_e               B1                  B2                  B3                  psi                 
error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       
5.18e-03  -         1.33e-02  -         7.05e-03  -         1.65e-02  -         7.95e-03  -         1.30e-02  -         7.93e-03  -         1.65e-02  -         2.54e-03  -         
4.50e-04  3.53      8.01e-04  4.05      4.66e-04  3.92      9.26e-04  4.15      2.80e-04  4.83      8.26e-04  3.98      4.63e-04  4.10      9.26e-04  4.15      2.99e-04  3.08      
2.76e-05  4.03      6.99e-05  3.52      3.86e-05  3.59      8.17e-05  3.50      1.08e-05  4.70      7.18e-05  3.52      4.03e-05  3.52      7.99e-05  3.53      3.21e-05  3.22      

mean      3.78      mean      3.79      mean      3.76      mean      3.83      mean      4.76      mean      3.75      mean      3.81      mean      3.84      mean      3.15      
----------------------------------------------------------------------------------------------------
linf
rho                 rho_v1              rho_v2              rho_v3              rho_e               B1                  B2                  B3                  psi                 
error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       error     EOC       
1.14e-02  -         3.23e-02  -         1.86e-02  -         5.64e-02  -         3.34e-02  -         4.37e-02  -         2.82e-02  -         5.62e-02  -         1.37e-02  -         
9.42e-04  3.60      3.07e-03  3.40      1.69e-03  3.46      3.55e-03  3.99      1.29e-03  4.70      3.45e-03  3.66      2.21e-03  3.68      3.52e-03  4.00      9.08e-04  3.92      
5.86e-05  4.01      2.50e-04  3.61      1.24e-04  3.77      3.01e-04  3.56      3.64e-05  5.14      2.73e-04  3.66      1.89e-04  3.54      2.73e-04  3.69      6.26e-05  3.86      

mean      3.80      mean      3.51      mean      3.62      mean      3.77      mean      4.92      mean      3.66      mean      3.61      mean      3.84      mean      3.89      
----------------------------------------------------------------------------------------------------
Dict{Symbol, Any} with 3 entries:
  :variables => ("rho", "rho_v1", "rho_v2", "rho_v3", "rho_e", "B1", "B2", "B3", "psi")
  :l2        => [3.7758, 3.78608, 3.75548, 3.82813, 4.76315, 3.75097, 3.81046, 3.84353, 3.15107]
  :linf      => [3.8024, 3.50665, 3.61503, 3.77391, 4.92067, 3.66201, 3.6093, 3.84236, 3.88718]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 78 lines in your changes missing coverage. Please review.

Project coverage is 95.93%. Comparing base (5185abd) to head (f4dd305).
Report is 103 commits behind head on main.

Files	Patch %	Lines
src/equations/visco_resistive_mhd_2d.jl	0.00%	47 Missing ⚠️
.../tree_2d_dgsem/elixir_mhd_diffusive_convergence.jl	0.00%	31 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1806      +/-   ##
==========================================
+ Coverage   89.67%   95.93%   +6.26%     
==========================================
  Files         458      462       +4     
  Lines       36400    37020     +620     
==========================================
+ Hits        32640    35515    +2875     
+ Misses       3760     1505    -2255     

Flag	Coverage Δ
unittests	95.93% <0.00%> (+6.26%)	⬆️

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