fix lua result serialization causing various issues

for example, loading a library which returns a table of functions would
fail with an inexplicable (to the user) error about serialization. This
is now fixed. We no longer use a single result type, instead there are
void results and normal results, and the former simply never has to
worry about the result.

This was likely causing even more issues; if the `sol::object` was
populated before, it hitting the dtor in another path would, again, like
we've seen before, corrupt the lua stack.

src/TPluginMonitor.cpp

@@ -70,7 +70,7 @@ void TPluginMonitor::operator()() {
                             auto Res = mEngine->EnqueueScript(StateID, Chunk);
                             Res->WaitUntilReady();
                             if (Res->IsError()) {
-                                auto Snapshot = Res->GetDetachedSnapshot();
+                                auto Snapshot = Res->GetSnapshot();
                                 beammp_lua_errorf("Error while hot-reloading \"{}\": {}", Pair.first, Snapshot.ErrorMessage);
                             } else {
                                 mEngine->ReportErrors(mEngine->TriggerLocalEvent(StateID, "onInit"));