This PR mainly changes:
1. Change the define of PBlock
The new PBlock consists of a set of PColumnMeta and a binary buffer.
The PColumnMeta records the metadata information of all columns in the Block,
while the buffer stores the serialized binary data of all columns.
2. Refactor the serialize/deserialize method of data type
Rewrite the `serialize()/deserialize()` of IDataType. And also add
a new method `get_uncompressed_serialized_bytes()` to get the total length
of uncompressed serialized data of a column.
3. Rewrite the serialize/deserialize method of Block
Now, when serializing a Block to PBlock, it will first get the total length
of uncompressed serialized data of all columns in this Block, and then allocate
the memory to write the serialized data to the buffer.
4. Use brpc attachment to transmit the serialized column data
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