feat: add default client when requested by the test case

[laurentsenta]

Fix #21

• When a test case expects more than one parameter (runenv), the js sdk will create a default sync client and pass it to the test,
• The client will be used as a signal emitter, which makes sure that the test's start, success, and failure events are sent to the sync service.
• This mimics the behavior of InitializedTestCaseFn in sdk-go.