WIP: Jin Xin Relaxation

[gregorgassner]

Playing around with Jin Xin relaxation approach, at the moment for compressible Euler 2D...

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 10.86957% with 164 lines in your changes are missing coverage. Please review.

Project coverage is 81.85%. Comparing base (5359525) to head (accbecb).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/equations/jin_xin_compressible_euler_2d.jl	0.00%	91 Missing ⚠️
src/callbacks_stage/positivity_zhang_shu_dg2d.jl	0.00%	63 Missing ⚠️
examples/tree_2d_dgsem/elixir_jin_xin_euler.jl	0.00%	9 Missing ⚠️
src/callbacks_stage/positivity_zhang_shu.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1666       +/-   ##
===========================================
- Coverage   96.11%   81.85%   -14.26%     
===========================================
  Files         460      462        +2     
  Lines       36926    37080      +154     
===========================================
- Hits        35490    30349     -5141     
- Misses       1436     6731     +5295     

Flag	Coverage Δ
unittests	81.85% <10.87%> (-14.26%)	⬇️

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