restore typing in tests and docs, remove unused metaclass code

docs_src/models/docs009.py

@@ -1,9 +1,21 @@
+from typing import Optional
+
+import databases
+import sqlalchemy
+
+import ormar
+from .docs010 import Artist  # previous example
+
+database = databases.Database("sqlite:///test.db", force_rollback=True)
+metadata = sqlalchemy.MetaData()
+
+
 class Album(ormar.Model):
     class Meta:
         tablename = "music_albums"
         metadata = metadata
         database = database
 
-    id = ormar.Integer(name='album_id', primary_key=True)
-    name = ormar.String(name='album_name', max_length=100)
-    artist= ormar.ForeignKey(Artist, name='artist_id')
+    id: int = ormar.Integer(name="album_id", primary_key=True)
+    name: str = ormar.String(name="album_name", max_length=100)
+    artist: Optional[Artist] = ormar.ForeignKey(Artist, name="artist_id")