[2.x] fix: Route queued jobs at push time instead of via a shared static $onQueue

[imorland]

The problem

AbstractJob::$onQueue is a static property on AbstractJob. A subclass that doesn't redeclare a static shares its parent's storage — so every job extending AbstractJob without its own $onQueue shares one slot. Routing two job classes collides (last write wins), and the same class can resolve differently across processes. In practice jobs silently land on whichever queue was assigned last. (The pattern dates back to 1.x's $sendOnQueue.)

The fix

Route jobs by class at push time, using Laravel's native queue-route manager.

• queue.routes — bind Laravel's Illuminate\Queue\QueueRoutes, which resolves a job's queue by its class and hierarchy (parents, interfaces, traits).
• Extend\Queue->route(JobClass::class, 'queue') — populates it. Routing an abstract/base class covers all subclasses; most specific wins.
• RoutingQueue wraps flarum.queue.connection: on push()/later()/bulk() with no explicit queue, it applies the route. Laravel only applies routes via the bus dispatcher (dispatch()), but most of Flarum and its extensions use the low-level push() — the wrapper closes that gap so push() routes too. It's applied in QueueServiceProvider::boot(), wrapping whatever connection extensions bind (FoF Redis / Horizon), so routing is driver-independent.

The sync driver is left unwrapped (it runs jobs inline, so routing is moot) — which also preserves the instanceof SyncQueue checks used to detect "no real queue". The two instanceof DatabaseQueue checks unwrap via RoutingQueue::getDriver().

use Flarum\Extend;

return [
    (new Extend\Queue())
        ->route(\Your\Extension\Jobs\SendExportJob::class, 'exports'),
];

Breaking change

AbstractJob::$onQueue is removed; code that set it moves to Extend\Queue::route(). This PR migrates the bundled GDPR and Realtime extensions and updates the GDPR README.

Tests

• RoutingQueueTest (unit): routing, explicit-queue-wins, unregistered pass-through, sibling classes independent, abstract-base routing, most-specific wins, later()/bulk(), string-job pass-through.
• QueueTest (integration): Extend\Queue populates queue.routes, extenders compose.
• QueueServiceProviderTest: the connection is a RoutingQueue wrapping the database driver.

Full core integration suite (760 tests) passes; GDPR + Realtime suites pass.

Docs: flarum/docs#565.