如何扩展并行网关

看了流程执行逻辑里，不管是getUniqueNextNode方法还是calculateNextNode方法，都是需要明确走到下一个确定的节点，那如何扩展并行网关

Start by reading the flow execution logic around getUniqueNextNode and calculateNextNode. Determine how the current implementation selects a single next node and what parallel-gateway behavior would require. The issue does not define the intended semantics, affected files, tests, or a completion criterion, so clarification is needed before implementation.

Written by the indexing model from the issue text.