Function build_timestamp_array 

fn build_timestamp_array<T: ArrowPrimitiveType<Native = i64>>(
    rows: &Rows,
    col_idx: usize,
    column_name: &str,
    row_count: usize,
    target_unit: TimeUnit,
) -> Result<ArrayRef>

Builds a timestamp array of T’s unit from a proto column, appending each value directly into the builder. Values already in the target unit are appended without conversion (the unchanged-unit fast path); others are converted via Timestamp::convert_to, flooring on narrowing.