Function build_temporary_state

pub(crate) fn build_temporary_state(
    row_state: &mut [Datum],
    is_finished: bool,
    current_pos: &OwnedRow,
    row_count: u64,
)

We want to avoid allocating a row for every vnode. Instead we can just modify a single row, and dispatch it to state table to write. This builds the following segments of the row:

1. current_pos
2. backfill_finished
3. row_count