Parallel iteration support

[Robin-Dong]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

Executing iterations for an LLM node sequentially can be slow when the number of iterations is large. Can we execute the iteration elements in parallel? maybe add a concurrency parameter for iteration node？

2. Additional context or comments

No response

3. Can you help us with this feature?

• I am interested in contributing to this feature.