beginTransaction method
Begins a new transaction with the specified isolation level.
The connectionId must be a valid active connection.
The isolationLevel should be a numeric value (0-3) corresponding
to isolation level enum values (0=ReadUncommitted, 1=ReadCommitted,
2=RepeatableRead, 3=Serializable).
Returns a transaction ID on success, 0 on failure.
Implementation
int beginTransaction(int connectionId, int isolationLevel) =>
_native.transactionBegin(connectionId, isolationLevel);