select decision columns using inspection-cost heuristics

examples/protocol-complete.tess

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+data State = Idle | Waiting | Connected
+
+data Message = Hello Int | Data Int | Close
+
+match classify (s : State) (m : Message) : Int =
+  | Idle (Hello n) -> n
+  | Idle (Data n) -> n
+  | Idle Close -> 0
+  | Waiting (Hello n) -> n
+  | Waiting (Data n) -> n
+  | Waiting Close -> 0
+  | Connected (Hello n) -> n
+  | Connected (Data n) -> n
+  | Connected Close -> 0