Default retry behavior causes infinite event loop on error

There's a flaw in the default retry behavior on [line 59](https://github.com/amplitude/Amplitude-Node/blob/main/packages/node/src/retry/defaultRetry.ts#L59): whenever an error occurs, a new call stack is created and we immediately return.

Instead of returning, we should `await this._onEventsError` here and ensure that onEventsError is a promise.

Currently waiting for amplitude.flush causes the node.js event loop to never clear in the case of a rate limit error.

Here's an example integration test without a rate limit using jest:

And here's one with a rate limit, notice how jest never exits: