SqliteVtabBeginCallback
This method begins a transaction on a virtual table. This method is optional. The xBegin pointer of sqlite3_module may be NULL.
This method is always followed by one call to either the xCommit or xRollback method. Virtual table transactions do not nest, so the xBegin method will not be invoked more than once on a single virtual table without an intervening call to either xCommit or xRollback. Multiple calls to other methods can and likely will occur in between the xBegin and the corresponding xCommit or xRollback.