feat: Add Discontinuous Galerkin (DG) discretization on Bernstein-Bézier tetrahedra and apply it to the acoustic wave propagator via SIPDG (Symmetric Interior Penalty DG)

[sframba]

• Create BB_Tetrahedron element and all matrices needed for IPDG acoustic 2nd order wave propagator
• Cleanup BB_Tetrahedron element
• Add new discretization formulation and corresponding dispatch
• Create AcousticWavePropagationDG solver
• Add and test mass, stiffness, damping, penalty and flux matrices
• (optional) Finalize basis element for other solvers, adding the needed matrices (e.g., anisotropic stiffness, ...)
• (optional) Create SIPDG version of other 2nd order wave propagators