`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 launchbadge/sqlx#3886 is merged.