SMLv3: sml::variant<> must match sml::sm.states_ ordering

[jmcmullan]

The sml::variant<> must match the implicit ordering of the sml::sm.state_ member, or the wrong state will be decoded (as there is no causal relationship between an instanced sml::variant<> and the implicitly instanced sml::variant<> in the state machine sml::sm<> class)

The following diff illustrates this issue, by simply reordering the <s1, s2> types in the NTEST self-test (which then breaks the NTEST).

I'm at a loss as how to work around this given the current SMLv3 architecture (as at sml::overload{} constructor time, the sml::sm<> class doesn't exist).

diff --git sml sml
--- a/sml
+++ b/sml
@@ -602,12 +602,12 @@ static_assert(([] {
     unsigned calls{};
 
     sml::sm sm = sml::overload{
-      [&](s1, const e& event) -> sml::variant<s1, s2> {
+      [&](s1, const e& event) -> sml::variant<s2, s1> {
         if (event.value) {
           ++calls;
           return s2{};
         }
-        return {};
+        return s1{};
       },
     };