Adding a particle resolution.

If the ParticleCut and the energy from which particles are treated stochastically differ very much, the propagation becomes very inefficient, although the physical result differs only little or not at all.

For this purpose an energy is introduced following MR !303 (merged) from which losses are taken into account stochastically. This can shorten the running time very much at high energy cuts.

The name "resolution" is debatable, but I find it pregnant and short.

tests/framework/testParticles.cpp

@@ -88,13 +88,18 @@ TEST_CASE("ParticleProperties", "[Particles]") {
           (Approx(2.1970332555864364e-06).epsilon(1e-5)));
   }
 
-  SECTION("Energy threshold") {
+  SECTION("Energy thresholds") {
     //! by default energy thresholds are set to zero
-    CHECK(get_kinetic_energy_propagation_threshold(Electron::code) == 0_GeV);
-
+    CHECK(get_kinetic_energy_propagation_threshold(Electron::code) == 1_GeV);
     set_kinetic_energy_propagation_threshold(Electron::code, 10_GeV);
     CHECK_FALSE(get_kinetic_energy_propagation_threshold(Code::Electron) == 1_GeV);
     CHECK(get_kinetic_energy_propagation_threshold(Code::Electron) == 10_GeV);
+
+    //! by default energy thresholds are set to zero
+    CHECK(get_energy_production_threshold(Neutron::code) == 1_MeV);
+    set_energy_production_threshold(Neutron::code, 1_GeV);
+    CHECK_FALSE(get_energy_production_threshold(Code::Neutron) == 1_MeV);
+    CHECK(get_energy_production_threshold(Code::Neutron) == 1_GeV);
   }
 
   SECTION("Particle groups: electromagnetic") {