Make IcebergSplitSource generate splits asynchronously

[lirui-apache]

The current IcebergSplitSource::getNextBatch is synchronous by returning a completed future. I wonder if there're specific reasons why it's implemented this way and whether we can make it asynchronous.

Some background: we made our iceberg use a blocking queue when planning files (in order to reduce memory consumption). Then if multiple-stage query run concurrently in trino, it can run into some kind of dead lock, because the stage scheduler can be blocked at IcebergSplitSource::getNextBatch while the thread pool used in planning files is occupied by other stages.

[findinpath]

This request is probably handled by apache/iceberg#10691

[lirui-apache]

Yes, I think this is not needed anymore, closing it