Set scopa targets to their traditional defaults

Partnership games go to 21: scopone scientifico (the tournament target)
and scopa a quattro, while two-player scopa keeps its usual 11. The scopa
package resolves the default from the player count and exposes a per
variant options_schema default, so the lobby creation form shows the
right value without frontend changes.

server/packages/tavolo-scopone/tests/test_plugin.py

@@ -35,7 +35,8 @@ class CreateTest(unittest.TestCase):
         session = _session(engine)
         self.assertEqual("A", session.players[0].team)
         self.assertIsInstance(session.state, ScoponeState)
-        self.assertEqual(11, session.state.target_score)
+        # The traditional partnership target.
+        self.assertEqual(21, session.state.target_score)
         self.assertTrue(session.state.napola)
 
     def test_create_options(self) -> None: