Comet Native Executors: run LIMIT and top-K queries with a per-partition limit before the exchange #7365

What is the problem the feature request solves?

On a Comet Native Executor cluster (#7289), a query with LIMIT, including Dataset.show(), fails: CometCollectLimitExec performs its own shuffle to one partition inside doExecuteColumnar, so it is not a native block, and the driver's stage-graph builder refuses it with "it does not run natively".

CometTakeOrderedAndProjectExec has the same shape. The prototype special-cases it as a stage that reads its child through a single-partition exchange and runs Comet's final top-K plan. Unless the child is a CometLocalTopKExec, the child's whole output crosses that one-partition exchange, where Comet on Spark runs a per-partition top-K first.

Describe the potential solution

Plan both operators as explicit native pieces, as Spark plans LocalLimit, then an exchange, then GlobalLimit: a block with a per-partition limit or top-K, a CometShuffleExchangeExec to a single partition, and a block with the final limit or top-K. The generic stage-graph builder then handles them without a special case, and only the first rows of each partition cross the exchange.

Additional context

The special case is takeOrderedStage in CometNativeExecutorsExec.scala. It calls finalNativePlan(inputPartitions = 2) only to select the sorting branch.

Part of #7288.

Willingness to contribute

Yes. I can contribute this feature independently.