refactor(express-wrapper): avoid using codec type-guard

This refactor changes the response code path to try encoding the
service function's response value with the apiSpec's response codec,
and if this errors returns a 500.

Previously we used the codec's type-guard as a test if the codec
can encode the service function's response value, but this step will
take extra time and there's no hard contract that guarantees us the
type-guard returning `true` really means that the codec will be able
to encode a value. Instead, we just try the dangerous deed and do our
best to catch errors.

Author: ericcrosson-bitgo

packages/express-wrapper/src/response.ts

@@ -38,13 +38,12 @@ export const defaultResponseEncoder: ResponseEncoder = (
     return;
   }
   const responseCodec = route.response[status];
-  if (responseCodec === undefined || !responseCodec.is(payload)) {
+  try {
+    expressRes.status(status).json(responseCodec!.encode(payload)).end();
+  } catch {
     console.warn(
       "Unable to encode route's return value, did you return the expected type?",
     );
     expressRes.status(500).end();
-    return;
   }
-
-  expressRes.status(status).json(responseCodec.encode(payload)).end();
 };