fn seek_to(&mut self, idx: usize) {
        if idx >= self.block.offsets.len() {
            self.key.clear();
            self.value_range = (0, 0);
            return;
        }
        let offset = self.block.offsets[idx] as usize;
        self.seek_to_offset(offset);
        self.idx = idx;
    }
Seeks to the idx-th key in the block.
mini-lsm-mvcc/src/block/iterator.rs