Port from QwenLM/qwen-code#11723: attaching the configured zone to croniter's
naive wall-clock result resolves the repeated autumn hour to its earlier
occurrence (fold=0), so a base inside the second occurrence received a
next_run_at up to an hour in the past — the fire path would treat it as due
immediately and loop. Try both folds of each candidate and return the earliest
instant strictly after the base; wall-clock jobs still fire exactly once on
the repeated hour (Vixie cron semantics).
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