test: reopen mnode unitest

feat(query): add the merge join operator for child table inner join.

refactor: vnode

enh(query): add an new internal api to extract query result timestamp precision before the query response received from dnode.

* [TD-13558]<feature>: taos shell refactor

add taosTools as submodule

* add tools/taos-tools

* add more client interface for taosTools compile

* update taos-tools

* update taos-tools

* refactor shell

* [TD-13558]<feature>: taos shell test speed

* [TD-13558]<feature>: taos -n startup works

* taos -n rpc works

* taos -n server works

* cleanup code since no endPort in 3.0

* update taos-tools

* [TD-13558]<feature>: taos -C works

* improve taos shell -c WIP

* update taos-tools

* add demoapi.c

* adjust show databases result for 3.0

* test: add platform logic

* add nchar

* adjust taos_fetch_lengths

* print fields

* remove show databases check from insert cases

* fix lua example compile for 3.0

still not work

feat: add heartbeat and performance_schema tables

fix(os): const ptr is passed to free()

feat(query): support now()/today() function in select clause