* test/e2e: replace sleeps with event-driven waits in chaos/group/store tests
Replace 21 time.Sleep calls with deterministic waiting using
WaitForOutput, WaitForTCPReady, and a new WaitForTCPUnreachable helper.
Add CountOutput method for snapshot-based incremental log matching.
* test/e2e: validate interval and cap dial/sleep to remaining deadline in WaitForTCPUnreachable