uncover bug by using more realistic configs in custom gates test

src/lib/pickles/test/optional_custom_gates/pickles_test_optional_custom_gates.ml

@@ -378,16 +378,28 @@ let register_feature_test (name, specific_feature_flags) =
 
 let () =
   let configurations =
-    [ ("xor", Plonk_types.Features.{ none_bool with xor = true })
+    [ ( "xor"
+      , Plonk_types.Features.{ none_bool with xor = true; range_check0 = true }
+      )
     ; ( "range check 0"
       , Plonk_types.Features.{ none_bool with range_check0 = true } )
     ; ( "range check 1"
       , Plonk_types.Features.{ none_bool with range_check1 = true } )
     ; ("rot", Plonk_types.Features.{ none_bool with rot = true })
     ; ( "foreign field addition"
-      , Plonk_types.Features.{ none_bool with foreign_field_add = true } )
-    ; ( "foreign field multiplication"
-      , Plonk_types.Features.{ none_bool with foreign_field_mul = true } )
+      , Plonk_types.Features.
+          { none_bool with
+            foreign_field_add = true
+          ; range_check0 = true
+          ; range_check1 = true
+          } )
+    ; ( "foreign field multiplication" (* FIXME: this configuration fails *)
+      , Plonk_types.Features.
+          { none_bool with
+            foreign_field_mul = true
+          ; (* toggling this to `false` makes the test succeed *)
+            range_check0 = true
+          } )
     ; ( "Fixed lookup tables"
       , Plonk_types.Features.{ none_bool with lookup = true } )
     ]