client: avoid unconsumed channel in timer construction

This PR fixes a bug introduced in #11983 where a Timer initialized with 0
duration causes an immediate tick, even if Reset is called before reading the
channel. The fix is to avoid doing that, instead creating a Timer with a non-zero
initial wait time, and then immediately calling Stop.

client/allocrunner/taskrunner/task_runner.go

@@ -563,7 +563,9 @@ func (tr *TaskRunner) Run() {
 	// Set the initial task state.
 	tr.stateUpdater.TaskStateUpdated()
 
-	timer, stop := helper.NewSafeTimer(0) // timer duration calculated JIT
+	// start with a stopped timer; actual restart delay computed later
+	timer, stop := helper.NewSafeTimer(999 * time.Hour)
+	timer.Stop()
 	defer stop()
 
 MAIN: