[2.x] fix: avoid duplicate ModelNotFoundException logs on orphaned queued jobs

[imorland]

Summary

When a queued job's serialized model is deleted between dispatch and worker pickup (a common race for notification fan-out — mentions, subscriptions, FoF byobu/follow-tags, etc.), the worker logs two ModelNotFoundException entries even though the race is handled correctly.

The flow (CallQueuedHandler):

1. Worker unserialize()s payload → firstOrFail() throws ModelNotFoundException (caught silently).
2. handleModelNotFound() runs. With deleteWhenMissingModels unset (default false), it falls through to $job->fail($e).
3. fail() calls getCommand() → unserialize() again → ModelNotFoundException (this time not caught, gets logged).

Setting public bool $deleteWhenMissingModels = true; on AbstractJob makes the handler $job->delete() the job instead, skipping the noisy second-deserialize path. The job is already off the queue and any unique-job lock has already been released.

Fixes #4615

Why apply at the AbstractJob level

All current AbstractJob subclasses (12 across core + bundled extensions) follow the same pattern: notify-X-about-Y, send-mail-about-Y, index-Y-for-search, run-composer-command, gdpr-export-for-user, etc. None of them does anything useful if the subject model has been deleted — there's no meaningful retry path.

Subclasses that genuinely want the failed-and-retry behavior can opt out with public bool $deleteWhenMissingModels = false;.

Changes

• framework/core/src/Queue/AbstractJob.php — set public bool $deleteWhenMissingModels = true; with a docblock explaining the override path.

Test plan

• Manual: dispatch a queued job whose model is then deleted before the worker reaches it (post a reply that triggers a notification, immediately delete the post). Confirm only the original ModelNotFoundException is logged once at INFO/DEBUG level (Laravel's caught-and-handled path), not twice at ERROR.
• Existing queue test suite passes.

Notes

• Pairs with [2.x] fix: add missing getHidden() to Log\Context\Repository stub #4633 (getHidden() stub fix) — once that's merged, this PR removes the remaining log noise from the same orphaned-job scenario.
• This is a behavior change for any third-party extension whose AbstractJob subclass was relying on failed() being called on missing models. That should be vanishingly rare given Flarum's job patterns, and the override is one line. Worth calling out in upgrade notes.