feat: capture O variable in gate for external range checker (#1211)

* feat: capture both L,R variables in same gate

* feat: capute O variable in gate

frontend/cs/scs/builder.go

@@ -729,12 +729,14 @@ func (builder *builder) GetWireConstraints(wires []frontend.Variable, addMissing
 		if _, ok := lookup[int(c.XA)]; ok {
 			res = append(res, [2]int{nbPub + constraintIdx, 0})
 			delete(lookup, int(c.XA))
-			continue
 		}
 		if _, ok := lookup[int(c.XB)]; ok {
 			res = append(res, [2]int{nbPub + constraintIdx, 1})
 			delete(lookup, int(c.XB))
-			continue
+		}
+		if _, ok := lookup[int(c.XC)]; ok {
+			res = append(res, [2]int{nbPub + constraintIdx, 2})
+			delete(lookup, int(c.XC))
 		}
 		if len(lookup) == 0 {
 			// we can break early if we found constraints for all the wires