Improve shared_ptr/reference/raw usage in tests functions

[JasonMarechal25]

          This helper class is clearly not an owner of the BC: we should provide it a reference instead of shared_ptr.

(possibly for later work since it has not been done in this PR)

Originally posted by @sylvlecl in https://github.com/AntaresSimulatorTeam/Antares_Simulator/pull/1388#discussion_r1278929930