Refactor m_riemann_solvers Module (HLLC Solver Subroutine) (#912)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Spencer Bryngelson <sbryngelson@gmail.com>
Co-authored-by: Malmahrouqi3 <mohdsaid497566@gmail.com>

Author: 4 people