Dedicated process for some test cases.

Most NTS files are self contents, but for some test cases, particular work is done in 'Fortran' files compiled after the Notus library compilation. The directory src/lib/test_cases is dedicated to this specific 'Fortran' V&V process and contains:

enumeration of the test cases names in enum.f90 that require 'Fortran' routines
definition of common variables variables.f90
the basic ('high-level') procedures that orients the program towards the correct test case are described in the V&V test cases processing page
a verification and a validation directories which have the same architecture of the corresponding root test_cases directory that contains the NTS files. Fr test cases that need special treatments that cannot be done with an NTS file, specific Fortran routines may exist ('reference solution', 'next iteration', 'post process' or 'prepare').

Note: this should be implemented using a UDF instead.