Refactor GRHD project

Major rework of GRHD project to include new broadcasting interface. The goal is to get a TOV evolution with the AV method.

PR contains various refactors:

• initialdata/: We promote this to a separate env in order to add CairoMakie for plotting.
• refactored and improve initialdata/SphericalAccretion.jl solver so that it agrees with various references: solver from bugner's thesis (extract from bamps), plots from two papers from Papadoulos.
• refactored initialdata/TOV.jl to not depend on dg1d.jl anymore, instead use OrindaryDiffEq and CairoMakie for plots
• copy of cons2prim from SRHD. these two versions should be merged eventually, but will do in a separate PR
• implement spherical1d formulation: this is a rewrite of the evolution GRHD equations to work with non-zero radial shift vector. this is needed to evolve the spherical accretion test in cowling approximation where there should be no dynamics.
• implement rescaled_spherical1d formulation: this is a rewrite of the previous formulation based on the generalized Valencia formulation (cf. Montero, Baumgarte paper from 2017); the auxiliary metric is chosen such that coordinate singularities at r=0 in the source terms are cancelled; doesn't work atm
• allow the spherical1d to include r=0 in the domain by using symmetry conditions to evaluate source terms at r=0 (workaround for rescaled_spherical1d not working right now)
• new ref tests: bondi accretion and TOV star
• implement a differentiate! method on Mesh in order to compute derivatives by hand, if needed

src/GRHD/cons2prim.jl

@@ -90,13 +90,13 @@ end
 #######################################################################
 
 
-@with_signature [simd=false] function cons2prim_kastaun(equation::AbstractEquation)
+@with_signature [simd=false] function cons2prim(equation::AbstractEquation)
   @accepts D, Sr, τ, r
   @accepts γrr
   D, Sr, τ, ρ, vr, ϵ, p = cons2prim_kastaun_impl(equation, D, Sr, τ, r, γrr)
   @returns D, Sr, τ, ρ, vr, ϵ, p
 end
-@with_signature [simd=false] function cons2prim_kastaun_rescaled(equation::AbstractEquation)
+@with_signature [simd=false] function cons2prim_rescaled_spherical1d(equation::AbstractEquation)
   @accepts D, Sr, τ, r
   @accepts A, B
   γrr = 1/B^2