feat(scantask-2): Implement new module for splitting Parquet ScanTask

[jaychia]

Implements a new module daft-scan/src/scan_task_iters/split_parquet which contains all the functionality for splitting an iterator of ScanTasks into smaller ScanTasks if they are Parquet files.

The public interface is SplitParquetScanTasks, which under the hood uses private functionality in the form of DecideSplitIterator -> RetrieveParquetMetadataIterator -> flatten to produce a new (split) iterator of ScanTasks.