Remove all PUE related CRONs on Site Kit reset and before Site Kit is setup

[zutigrm]

Feature Description

Currently we are not unscheduling/removing Email Reporting CRON's when FF is disabled. Also it seems Email Reporting CRON's are added even before SIte Kit is setup

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Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

• When proactiveUserEngagement feature flag is disabled all Email Reporting CRON's are removed
• When Site Kit is not set up, no Email Reporting CRON should be scheduled - Email reports should only be scheduled, at minimum, once Site Kit is set up.
• When Site Kit is reset all Email Reporting CRONs are removed

Implementation Brief

• Perform cleanup when the proactiveUserEngagement feature flag is disabled: during plugin bootstrap where proactiveUserEngagement is checked (in Plugin::register where Feature_Flags::enabled( 'proactiveUserEngagement' ) gates Email Reporting), add a branch for the disabled path that instantiates Email_Reporting_Scheduler (with Frequency_Planner) and calls unschedule_all() to clear googlesitekit_email_reporting_* cron hooks. This ensures any previously queued events are removed because the feature is no longer registered.
• Gate scheduling on setup completion: inject Authentication into the Email_Reporting class (pass it from Plugin::register alongside existing dependencies) and guard the scheduling logic in Email_Reporting::register() with $this->authentication->is_setup_completed(). If setup is incomplete, short-circuit before scheduling, and proactively call $this->scheduler->unschedule_all() to clean up any existing events.
• Preserve enable/disable toggle behavior: keep the existing is_email_reporting_enabled() checks, but require both "email reporting enabled" and "setup complete" before scheduling. If either is false (flag off, toggle off, or setup incomplete), ensure unschedule_all() runs so no cron remains registered.

Test Coverage

• Extend integration tests in tests/phpunit/integration/Core/Email_Reporting to verify:
  • When proactiveUserEngagement is disabled, any pre-scheduled email reporting cron events are removed via scheduler cleanup;
  • When Authentication::is_setup_completed() returns false, no new email reporting events are scheduled and existing ones are cleared.

QA Brief

• Verify that before setting up the Site Kit there are no email_reporting_* related CRONS (If previously there are some stale CRONs, remove them and reload the page, verify they are not being added)

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• Setup Site Kit
• Verify that email reporting CRONs are added - as Email reporting setting is enabled by default

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• Go to Settings > Admin Settings and disable Email Reporting
• Verify that Email Reporting CRONs have been removed

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• Go to Settings > Admin Settings and reset Site Kit
• Verify that Email Reporting CRONs are removed

Changelog entry

• Update the uninstall script to unregister all email reporting events when the plugin is unininstalled.