Scheduler: Process batches for individual hooks

[obenland]

Proposed changes:

• Adds specific event hooks for sending outbox items to followers and retries.
• Adds back-compat to existing events that still pass an event callback.
• Makes checks for existing jobs post-specific, since that's now possible.
• Removes next_scheduled_hook() method, as it is no longer used.
• Updates unit test.

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Update a post, create a comment, or update your user profile.
• Trigger registered events: npm run env -- run cli wp cron event run --all
• Make sure there are no errors or warnings and Outbox items still get processed as expected.
• Switch to trunk and generate events with the old signature (I defined ACTIVITYPUB_OUTBOX_PROCESSING_BATCH_SIZE = 1 to trigger batching)
• With events with the old signature scheduled, switch to this branch and run the events.

Changelog entry

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Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

Batch processing jobs can now be scheduled with individual hooks.

[obenland]

First pass. It'll need a bit more testing.

[pfefferle]

I will run some tests on my live system tomorrow morning.

[pfefferle]

I have the same issue when "flooding" the db with comments. It seems that only 2 of 5 to 7 comments will be queued properly. If I trigger the activitypub_reprocess_outbox process afterwards, all comments will be queued properly and also sent to all followers.

Might there be a flood control mechanism that still interferes somehow?

[obenland]

Yeah, I wouldn't expect this PR to help with that directly. But it should help with more fine-grain control over identifying specific jobs

[pfefferle]

Except from the flooding issue, everything seems to work as before... Have to check the retries though... I have no broken followers on my second blog 🫣

[pfefferle]

I have some really weird experiences on my live system. Have to observe that a bit.

[pfefferle]

Removed my changes... will think about logging in general...

[obenland]

@pfefferle I gave this another round of testing and it doesn't seem to show its age :)