Restores part of b3bf2e8a

This reverts commit b3bf2e8a.

Was meant to be a patch commit

See 07ea030a

Can't call `wp_trash_post()` before `init` because it relies on `wp_insert_post()`, which performs capabilties checks.

Core's normal handling would result in too many deletes at a time

Review feedback: trash posts for faster processing and deferred removal, and use a Core function to find an event as it can be used before init and includes caching

Also, explicitly reference secret from global scope, for consistency throughout plugin

Introduce utility method to replace many of the nested `foreach()` patterns needed to extract event data from the format Core uses

Uses Core functions to ensure the CPT hooks are performing as expected. Needs a corresponding test that checks the CPT directly.