pub fn seek_to_key(&mut self, key: KeySlice) {
        let mut low = 0;
        let mut high = self.block.offsets.len();
        while low < high {
            let mid = low + (high - low) / 2;
            self.seek_to(mid);
            assert!(self.is_valid());
            match self.key().cmp(&key) {
                std::cmp::Ordering::Less => low = mid + 1,
                std::cmp::Ordering::Greater => high = mid,
                std::cmp::Ordering::Equal => return,
            }
        }
        self.seek_to(low);
    }
Seek to the first key that is >= `key`.
mini-lsm/src/block/iterator.rs