perf(data-events): queue dispatches to execute on shutdown

[miguelpeixe]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

p1733922470397489-slack-C055SRT7WN4

Depending on the setup, a site can execute 5 dispatches when a reader registers:

• membership_status_active
• membership_saved
• reader_logged_in
• reader_registered
• network_user_updated

The list grows if the registration happens during a subscription purchase.

Other actions on the site can also dispatch multiple events.

Each dispatch runs a wp_remote_post(). Even though it's a non-blocking execution with a timeout of 0.01, calling this function for every dispatch is unnecessary and costs performance.

This PR proposes queueing the dispatches to be executed in a single wp_remote_post() called on the shutdown hook. This hook runs right before PHP shuts down execution, including on fatal errors.

How to test the changes in this Pull Request:

1. Make sure you have RAS configured and NEWSPACK_LOG_LEVEL set to at least 2 on wp-config.php
2. Add a webhook endpoint (https://webhook.site/ is your friend) assigned to the actions listed above
3. On a fresh session, register a new reader
4. Confirm you get the following log: (actions may vary according to your setup, but you should get at least reader_registered and reader_logged_in in the same run

Dispatching actions: "membership_status_active, membership_saved, reader_logged_in, reader_registered, network_user_updated".

5. Confirm you get the logs for handler execution as well:

[Newspack\Data_Events::handle]: Executing global action handlers for "membership_status_active".
[Newspack\Data_Events::handle]: Executing action handlers for "membership_status_active".
[Newspack\Data_Events::handle]: Executing global action handlers for "membership_saved".
[Newspack\Data_Events::handle]: Executing action handlers for "membership_saved".
[Newspack\Data_Events::handle]: Executing global action handlers for "reader_logged_in".
[Newspack\Data_Events::handle]: Executing action handlers for "reader_logged_in".
[Newspack\Data_Events::handle]: Executing global action handlers for "reader_registered".
[Newspack\Data_Events::handle]: Executing action handlers for "reader_registered".
[Newspack\Data_Events::handle]: Executing global action handlers for "network_user_updated".
[Newspack\Data_Events::handle]: Executing action handlers for "network_user_updated".

6. Wait until the webhook requests are processed and confirm every request reached your endpoint with the expected data

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?