Fix integration_test/test/live_connection/eval_and_inspect_test.dart flake

[elliette]

Work towards #8013

Tries to fix one of our top integration test flakes:

• example run: https://github.com/flutter/devtools/actions/runs/9716615461/job/26820586270

Actual: _TextContainingWidgetFinder:<Found 0 widgets with text
containing Variable button is created : []>
   Which: means none were found but one was expected

Evaluation is async since it requires a response from the VM service. I think this test was flaking because we were looking for the eval response in the console too soon. This PR adds and uses a test utility function (retryUntilFound) that will retry looking for a finder with a safePumpDuration in between until the found or there are no more retries.

[bkonyi]

How long is safePumpDuration?

[elliette]

3 seconds:

const shortPumpDuration = Duration(seconds: 1);
const safePumpDuration = Duration(seconds: 3);
const longPumpDuration = Duration(seconds: 6);
const veryLongPumpDuration = Duration(seconds: 9);

[bkonyi]

Thanks! That seems reasonable, I think.