Issue about non trivial on_entry/on_exit

[GuiCodron]

Expected Behavior

I don't really know what you want from non trivial on_exit/on_entry, but I thought it would pick the most specific on_exit/on_entry and avoid using the default one.

i.e. the following state machine:
struct c {
auto operator()() noexcept {
using namespace sml;
// clang-format off
return make_transition_table(
*idle + sml::on_exit<> / [this] { calls+="|"; }
,idle + sml::on_exit / [this] { calls+="e2|"; }
,idle + event = s1
,idle + event = s1
);
// clang-format on
}

std::string calls;

};

Triggering an event e2 should only add "e2|" and triggering e1 should add "_|".
Same expected behaviour if sm was inside a parent sm.

Actual Behavior

Triggering e2 add "e2|" and "_|"

Steps to Reproduce the Problem

1. checkout this version https://github.com/GuiCodron/sml/tree/gco/fix-non-trivial-entry-exit
2. Execute the following command from root directory
   mkdir -f BUILD && cd BUILD && rm -rf *; cmake .. && make test_transitions && ./test/ft/test_transitions
3. Test will fail with on_exit being called multiple times

I can work on this. But I would like to know what is the expected behaviour of non-trivial on_entry/on_entry?