IMAU-ice-and-climate/IMAU-FDM

AI Summary: Refactor the snow density parameterization subroutine in the IMAU-FDM Fortran code. The current implementation contains redundant code and uses different parameterizations for Antarctica and Greenland. The task involves deciding whether to keep both parameterizations or consolidate them into a single, more efficient approach, and then restructuring the subroutine for improved readability and maintainability.