[SAVer] Use Unknown instead of Invalid as SAVer is not complete.

src/SAVer.ml

@@ -138,7 +138,7 @@ let build_answer pred_kind prover_result =
       let prover_answer =
         if nb_total = nb_proved
         then Call_provers.Valid
-        else Call_provers.Invalid
+        else Call_provers.Unknown ""
       in
       { prover_answer; nb_total; nb_proved }
     | None -> failwith "Cannot interpret the output provided by SAVer")

tests/simple_ovo.t

@@ -38,5 +38,5 @@ Test verify
   > end
   > EOF
   [caisar] Goal G: Valid (2/2)
-  [caisar] Goal H: Invalid (1/2)
-  [caisar] Goal I: Invalid (0/2)
+  [caisar] Goal H: Unknown () (1/2)
+  [caisar] Goal I: Unknown () (0/2)