* [TD-3733]<fix>: taosdemo buffer processing refactor.

* [TD-3733]<fix>: taosdemo generate SQL head buffer process.

* [TD-3733]<fix>: taosdemo generate sql head buffer processing.

fix compile issue for windows.

* [TD-3733]<fix>: taosdemo generate sql head buffer processing.

fix max_sql_len. generate data buffer refactor.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>