SOLR-18252: Fix flaky test by avoiding race conditions.

[sigram]

This fixes a flaky test. ArrayList has been replaced with a BlockingQueue, plus used a better approach to consuming the records being collected in the queue.

[epugh]

I have recently used TimeOut, and I was wondering if there are any strong patterns in how we use, because I thoguht I had seen a streamlined pattern then how hyou used it. I asked Claude for some help, and it reminde me we have done a couple of lamda uses with timeout:

TimeOut t = new TimeOut(5000, TimeUnit.MILLISECONDS, TimeSource.NANO_TIME);
t.waitFor("Timeout waiting for c1", () -> reader.getClusterState().getCollectionOrNull("c1") != null);

Not sure if that is useful at all to you, but I appreciate your working on the flaky test!

[sigram]

@epugh looks nice, good to know. But in this case the lambda is relatively large so I think it would be less readable than this explicit loop.