make shock tube and blast wave tests run for SRHD when using MDA AV

The key step was to adapt a 'covariant' regularization that looks like

\partial_t D + \partial_x f_D^x = - \partial_x ( \mu ( \partial_t - \partial_x ) D ),

where the time derivative on the RHS is new compared to previous attempts. We approximate \partial_t D by the - \partial_x f_D^x.

Note that this is not truely covariant, but (\partial_t - \partial_x) ( \mu ( \partial_t - \partial_x ) D) would be. Problem is that we don't know how to approximate the second time derivatives or the mixed time-space derivatives. But it works this way, so leave it for now.

This PR adds example parameter files that allow to reproduce the SRHD tests from https://arxiv.org/pdf/2202.08839.pdf. To run the blastwave2 test it was important to add correct the evolved variable tau whenever the energy density eps turned slightly negative, as suggested in https://arxiv.org/pdf/2005.01821.pdf III.A. What is interesting is that atm we don't need an atmosphere description, but that's probably because those tests do not examine low densities.

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Side note: Realized that !75 (merged) promoted Mesh to a parameteric type and now most of the HRSC and TCI structs suffer from type instabilities. Need to fix this in a separate PR.

src/SRHD/initialdata.jl

@@ -525,6 +525,7 @@ end
 
 initialdata_smooth!(env, P::Project, mesh::Mesh{FVElement}) = nothing
 function initialdata_smooth!(env, P::Project, mesh)
+  !isregistered(mesh.cache, :mu) && return
   @unpack D, S, tau = get_dynamic_variables(mesh.cache)
   @unpack mu = get_cell_variables(mesh.cache)
   bernstein = BernsteinReconstruction(mesh)