Add a central non-conservative flux for 3D multi-ion MHD and a convergence test

[amrueda]

The new flux allows to use a standard LLF flux in 3D curvilinear grids

[github-actions]

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Testing

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Created with ❤️ by the Trixi.jl community.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.77%. Comparing base (1a987c4) to head (b3e0876).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2575      +/-   ##
==========================================
+ Coverage   90.85%   96.77%   +5.93%     
==========================================
  Files         521      522       +1     
  Lines       42443    42578     +135     
==========================================
+ Hits        38558    41204    +2646     
+ Misses       3885     1374    -2511     

Flag	Coverage Δ
unittests	96.77% <100.00%> (+5.93%)	⬆️

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[DanielDoehring]

Suggested change

	# (we multiply by 2 because the non-conservative flux is multiplied by 0.5 whenever it's used in the Trixi code)
	# Multiply by 2 because the non-conservative flux is multiplied by 0.5 in routines like `calc_interface_flux!`, `flux_differencing_kernel!` etc.

I find the "Trixi code" not really helpful

[DanielDoehring]

See above

[DanielDoehring]

Suggested change

	Returns a fraction (alpha) of the total ion pressure for the electron pressure.
	Returns a fraction (alpha) of the total ion pressure for the electron pressure.

I think we normally have an empty line here

[JoshuaLampert]

Suggested change

	let
	t = sol.t[end]
	u_ode = sol.u[end]
	du_ode = similar(u_ode)
	@test (@allocated Trixi.rhs!(du_ode, u_ode, semi, t)) < 1000
	end
	@test_allocations(Trixi.rhs!, semi, sol, 1000)

From #2571.