Function execute_prefilter 

pub(crate) async fn execute_prefilter(
    prefilter_ctx: &mut PrefilterContext,
    reader_builder: &RowGroupReaderBuilder,
    build_ctx: &RowGroupBuildContext<'_>,
) -> Result<PrefilterResult>

Executes prefiltering on a row group.

Reads only the prefilter columns (currently the PK dictionary column), applies filters, and returns a refined [RowSelection].