Simplify concurrent pull test

Remove the worker solution, simulate the concurrent pull by updating pending_since while PullingPendingTenant

tests/Etc/pull-worker.php

@@ -1,34 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/**
- * Worker for the "concurrent pulls" tests.
- * Separate OS process that boots the same test env and calls pullPendingFromPool().
- * Since multiple processes run at once, they race for the pool.
- *
- * Used like `php pull-worker.php <startAtUnixFloat> <firstOrCreate:0|1>`
- *
- * Outputs the key of the pulled tenant, or "null" if nothing was pulled.
- */
-
-require __DIR__ . '/../../vendor/autoload.php';
-
-use Stancl\Tenancy\Tests\Etc\Tenant;
-use Stancl\Tenancy\Tests\TestCase;
-
-$startAt = (float) ($argv[1] ?? 0);
-$firstOrCreate = ($argv[2] ?? '0') === '1';
-
-// createApplication() replays the suite's central-MySQL config without running setUp(),
-// so the pending tenants the parent test created survive into this process.
-(new class('pull-worker') extends TestCase {})->createApplication();
-
-// Wait so that every worker pulls at the same time
-if ($startAt > 0.0) {
-    time_sleep_until($startAt);
-}
-
-$tenant = Tenant::pullPendingFromPool($firstOrCreate);
-
-fwrite(STDOUT, $tenant?->getKey() ?? 'null');