implement FV method for Euler equation

Proof of concept. Can evolve now a sod shock tube problem.

This PR also updates the fv_update_step! methods to accept values for numerical flux and bdry values for u which can be computed so that boundary conditions different from periodic ones can be used.

Furthermore, this PR fixes the timestep computation for the AbstractHRSC methods, where previously we took too large of a time step.

added 1d bugfix equation feature labels

enabled an automatic merge when the pipeline for a1604e41 succeeds

merged

mentioned in commit a5f246be

mentioned in commit 89d47243