test: add unitest for sdb

feat: migrate tsdb read interface to vnode

fix(query): avoid to build dummy value column in group by constant value.

fix(retry): fix retry count

refactor: vnode

fix(rpc): taosd stuck when exiting the process

fix: memory error

enh: stream supports filter

fix: fix hb crash issue

enh: refactor unit test of parser and planner

test: case for math functions 

fix: subscrption api