Wait for polling queries in logging tests instead of sleeping

[wintan1418]

Related to #602

Problem

The "polling queries are logged" tests in WorkerTest and DispatcherTest start a worker/dispatcher and sleep for a fixed window (0.2s / 0.5s) before asserting that the polling SELECT shows up in the captured log. On a slow CI runner, process boot (DB registration, pool startup) can eat the whole window before the first poll executes, so the log only contains the process INSERT and the assertion fails.

Example failure from a recent CI run (MySQL job):

Failure:
WorkerTest#test_polling_queries_are_logged [test/unit/worker_test.rb:156]:
Expected /SELECT .* FROM .solid_queue_ready_executions. .../ to match
"  TRANSACTION (0.2ms)  BEGIN\n  SolidQueue::Process Create (0.5ms)  INSERT INTO `solid_queue_processes` ..."

Fix

Poll the captured log for the expected query with wait_while_with_timeout (3 seconds) instead of a flat sleep. The tests remain as fast as before in the common case — the wait returns as soon as the query appears — and become robust when the runner is slow. On timeout, the existing assertion still runs and reports the log contents.