pub fn new(block_size: usize) -> Self {
        Self {
            data: Vec::new(),
            meta: Vec::new(),
            first_key: KeyVec::new(),
            last_key: KeyVec::new(),
            block_size,
            builder: BlockBuilder::new(block_size),
            key_hashes: Vec::new(),
        }
    }
Create a builder based on target block size.
mini-lsm/src/table/builder.rs