…62804)

### What problem does this PR solve?

`InsertIntoTableCommand.applyInsertPlanStatistic` populated
`LoadStatistic.fileNum` from `FileScanNode.getSelectedSplitNum()`, i.e.
the BE **split count**, not the number of physical input files. When a
file crossed the split-size threshold (default
`max_initial_file_split_size × 1.1 ≈ 35.2MB`) and was cut into multiple
splits, both `jobs("type"="insert").LoadStatistic.FileNumber` and
`tasks("type"="insert").LoadStatistic.FileNumber` reported a value
larger than the actual file list. In the user-reported scenario, 8 input
files appeared as `FileNumber = 16` because each 42MB file was split in
two. Data correctness is unaffected; only the displayed statistic was
misleading.

This affects both streaming insert jobs and regular `INSERT INTO ...
SELECT FROM S3/HDFS/Hive`.