perf: BroadcastExchangeExec parent should not transformUp its children after conversion

[wForget]

What is the problem the feature request solves?

Currently, the BroadcastExchangeExec parent applies CometExecRule again after conversion, which will traverse all its children again.

datafusion-comet/spark/src/main/scala/org/apache/comet/rules/CometExecRule.scala

Line 449 in 9cac1af

val newPlan = apply(plan.withNewChildren(newChildren))

Describe the potential solution

No response

Additional context

No response