Add some type hints to datastore (#12423)

* Add some type hints to datastore

* newsfile

* change `Collection` to `List`

* refactor return type of `select_users_txn`

* correct type hint in `stream.py`

* Remove `Optional` in `select_users_txn`

* remove not needed return type in `__init__`

* Revert change in `get_stream_id_for_event_txn`

* Remove import from `Literal`