[Fix] Fix contract.Sequence reversing order (#1510)

* Fix contract.Sequence reversing order

This commit started by fixing tests that didn't fire, because they
involved contracts but were never executed. On of those tests failed
after being fixed, indicating that `std.contract.Sequence` wasn't
preserving the order of applied contracts. This commit fixes this issue
as well by using `fold_left` instead of `fold_right` in the
implementation of `Sequence`.

* Formatting (stdlib)

core/stdlib/std.ncl

@@ -968,7 +968,11 @@
           ```
         "%
       = fun contracts label value =>
-        std.array.fold_right (fun contract => std.contract.apply contract label) value contracts,
+        std.array.fold_left
+          (fun acc contract => std.contract.apply contract label acc)
+          value
+          contracts,
+
     label
       | doc m%"
           The label submodule provides functions that manipulate the label

core/tests/integration/pass/contracts/contracts.ncl

@@ -165,12 +165,17 @@ let {check, Assert, ..} = import "../lib/assert.ncl" in
   let f | forall r. { ; r } -> { g : forall r. { ; r } -> { z : Number ; r }; r }
         = fun r => %record_insert% "g" r g in
   let res = f { z = 3 }
-  in true,
+  in std.seq res true,
 
   # std.contract.Sequence
-  let three = 3 | std.contract.Sequence [ Number, std.contract.from_predicate (fun x => x < 5) ] in
-  # preserves order
-  let tag = "some_tag" | std.contract.Sequence [ std.enum.TagOrString, [| 'some_tag |] ]
-  in true
+  let SmallerThanFive = std.contract.from_predicate (fun x => x < 5) in
+  let three | std.contract.Sequence [ Number, SmallerThanFive] = 3 in
+  three == 3,
+
+  # std.contract.Sequence preserves order
+  let tag | std.contract.Sequence [std.enum.TagOrString, [| 'some_tag |]]
+    = "some_tag"
+  in
+  tag == 'some_tag,
 ]
 |> check