* [TD-3985]<fix>: taosdemo timestamp step overflow.

* fix specified subscribe test.

* replace potential overflow of int32 to int64

* replace potential int32 overflow variables to int64.

* replace potential int32 overflow variables to int64.

* change max of int16 to int64 after type changed.

* improve more.

* improve more and more.
Co-authored-by: NShuduo Sang <sdsang@taosdata.com>