`Executor::fetch_many` impl should error on arguments or persistence

[bobozaur]

The QueryAs::fetch method from sqlx calls Executor::fetch_many underneath, so this change cannot be done now. A test was implemented to check against this.

When this test starts failing, check again whether the Executor::fetch_many can be made to fail on multi-statement queries that have arguments or are meant to be prepared.

If all looks good, then Executor::fetch_many can be made to exclusively call ExecuteBatch and possibly error out when it would otherwise prepare a statement or bind arguments.

[bobozaur]

This could be implemented once transact-rs/sqlx#3886 is merged.

[bobozaur]

While this should in my opinion be the desired behavior, all sqlx drivers behave the same in this regard:

• if it's a single statement query it gets prepared and arguments, if present, are used
• if it's a multi statement query it just gets executed without being prepared, which implies not using the arguments

For the sake of consistency I'll leave it as-is for now. I also believe that the problem is rather rooted in sqlx itself and that, perhaps, the fetch_many and execute_many methods should instead accept a different interface, maybe something like ExecuteMany that simply does not even allow binding arguments. That would make a much clearer distinction of what can/can't be done and why as opposed to selecting the behavior and runtime.

[bobozaur]

Seems like this is an open topic for discussion already: transact-rs/sqlx#3108.