Reads one row of a vector (array) column named name from an open
parquet_reader (reader): values receives that row's full element
vector, selected by the 1-based row_index. Dispatched by values'
actual/declared type/kind, and separately by row_index's own kind
(integer(int32) or integer(int64) -- the latter needed only to address
a row beyond huge(1_int32), 2,147,483,647, in a file that large).
null_value (optional) fills missing entries; is_valid (optional)
reports which elements were actually present. See
parquet_read_array_element_mode for the complementary "one element
across all rows" access pattern. Reads only the one row group row_index falls in (not the
whole column), unless a row filter is active (parquet_open_reader(..., filter=)/
parquet_reader_set_filter), in which case row_index addresses the filtered result and the
whole (filtered) column is read -- mapping a filtered row index back to its physical row
group needs a per-row-group survivor count that this path does not yet use.