add executeMultiple for multi-statement strings

[stevenctl]

fixes #122

This PR adds a new method that allows executing all statements in a given string. More context is in the issue.

// bikeshedding on the name is very welcome!
Future<void> executeMultiple(String sql, [List<Object?> paramters = const []]) async

Based on feedback, I've updated the PR to just use execute which doesn't require any changes to the core sqlite3 package. However, I still believe this functionality needs a new API. It is valid to expect a ResultSet from the vanilla execute. I don't think there is a way to modify that signature to add settings here. The only way to avoid adding an API here

Also, using execute means that it is valid after all to pass parameters. Using params.isEmpty/isNotEmpty is probably not a good way to decide whether the user can expect a result back (it's perfectly valid to expect a result from INSERT INTO mytable (something) RETURNING id.

This is implemented using prepareMultiple from the sqlite3 package.

For web support, an additional PR (simolus3/sqlite3.dart#337) was required in that repo/package. For now I left a dependency override that should be removed before merging.

[simolus3]

Thanks for your contribution 👍

[stevensJourney]

Happy from my side with the changes