Add type hints to formatter

mautrix_telegram/formatter/__init__.py

@@ -1,8 +1,9 @@
 from .from_matrix import (matrix_reply_to_telegram, matrix_to_telegram, matrix_text_to_telegram,
                           init_mx)
 from .from_telegram import (telegram_reply_to_matrix, telegram_to_matrix, init_tg)
+from ..context import Context
 
 
-def init(context):
+def init(context: Context):
     init_mx(context)
     init_tg(context)