fix additional encoding issue for cursor with equals symbol. Add contract client return type. Add additional cursor e2e test.

src/constants/enum.ts

@@ -19,6 +19,7 @@ export const API_ERROR_CODE = {
   INVALID_API_KEY_OR_PERMISSIONS: 10003,
   SIGNATURE_NOT_VALID: 10004,
   INCORRECT_API_KEY_PERMISSIONS: 10005,
+  DB_ERROR_WRONG_CURSOR: 10016,
   INCORRECT_PRIVATE_OPERATIONS: 3303001,
   /** Account not unified margin, update required */
   ACCOUNT_NOT_UNIFIED: 10020,