Add psycopg2 as an optional dependency and throw error at startup if db is not initialized

mautrix_telegram/db/__init__.py

@@ -13,6 +13,8 @@
 #
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
+from sqlalchemy.engine.base import Engine
+
 from mautrix.bridge.db import UserProfile, RoomState
 
 from .bot_chat import BotChat
@@ -23,7 +25,7 @@ from .telegram_file import TelegramFile
 from .user import User, UserPortal, Contact
 
 
-def init(db_engine) -> None:
+def init(db_engine: Engine) -> None:
     for table in (Portal, Message, User, Contact, UserPortal, Puppet, TelegramFile, UserProfile,
                   RoomState, BotChat):
         table.db = db_engine