New output format for interaction histogram and simplifications

• with boost::histogram 1.74 things got simpler and the workaround treatment of nuclear projectiles is obsolete now (see https://github.com/boostorg/histogram/issues/279)
• no custom text output anymore, save_hist() is used now insted to save npz files.

Processes/InteractionCounter/InteractionHistogram.hpp

@@ -23,7 +23,6 @@ namespace corsika::process::interaction_counter {
     inline auto hist_factory(unsigned int bin_number, float e_low, float e_high) {
       namespace bh = boost::histogram;
       namespace bha = bh::axis;
-      using namespace units::si;
 
       auto h = bh::make_histogram(
           bha::category<int, bh::use_default, bha::option::growth_t>{{2212, 2112},