Improve `SELECT text` performance

[kou]

It's slower than the PostgreSQL protocol.

The followings may be related but we need to look into it:

• Building arrow::RecordBatch is slow?
  • We need to build arrow::RecordBatches to use arrow::ipc::RecordBatchWriter(). We need to copy PostgreSQL data for it. (Not zero-copy.)
  • Should we add an API that writes Apache Arrow streaming format data without building arrow::RecordBatch to Apache Arrow C++?
• Calling SPI_getbinval() is slow?
  • It calls nocachegetattr() https://github.com/postgres/postgres/blob/3edc6580c0e27fb8f13322efd255a88d20dda6c2/src/backend/access/common/heaptuple.c#L496-L712 and it's not a short function. Can we shortcut some operations?