refactor: add session id to prepare funcs

Summary

• refactor: add session id to prepare funcs

1. add session id argument to sql_prepare_ext
2. introduce sql_unprepare_ext function. This function removes prepared stmt using given session id.

In picodata SQL, we may prepare stmt in one session and unprepare it in some other session, which does not know in what session the statement was prepared. Now sql_prepare_ext returns not only statement id, but also a session id. This way statement can be unprepared from other session using sql_unprepare_ext.

NO_DOC=picodata internal patch NO_CHANGELOG=picodata internal patch

Close #... Docs follow-up: not necessary / new issue