Fixes #1349.

(*consumerSession).listOrEpoch requeued a failed offset load from an unconditional defer:

defer s.decWorker()
defer reloads.loadWithSession(s, "reload offsets from load failure")
after := time.NewTimer(time.Second)
defer after.Stop()
select {
case <-after.C:
case <-s.ctx.Done():
    return
}

When the session context is canceled (group leave during Close), the select returns at once but the deferred loadWithSession still requeues the load. The requeued listOrEpoch runs with the same canceled context, fails, and requeues again with no backoff. The busy loop keeps a session worker alive, so stopSession never sees workers == 0 and Close hangs.

This regressed in 6c7aab5, which removed the session-context early return from the drain loop. Before that, a canceled session returned before reloads was populated.

The fix only requeues when the backoff timer fires and returns without requeuing once the session context is done. Added TestIssue1349 in kfake, which hangs without the fix.