🐛 using backwards compatible types.Optional

- instead more modern `| None`

tomato_cooker/models/cost_based/cost_based.py

@@ -1,5 +1,5 @@
 import dataclasses
-from typing import ClassVar
+from typing import ClassVar, Optional
 from pathlib import Path
 from ..base import GridProblem
 
@@ -14,9 +14,9 @@ class TimetableScenario(GridProblem):
     days: list[str] = dataclasses.field(default_factory=lambda: [dl, dm, dx, dj, dv])
     nHours: int = 4
     nLines: int = 6
-    forced: list[list[set[str]]] | None = None
-    busy: list[list[set[str]]] | None = None 
-    undesired: list[list[set[str]]] | None = None
+    forced: Optional[list[list[set[str]]]] = None
+    busy: Optional[list[list[set[str]]]] = None
+    undesired: Optional[list[list[set[str]]]] = None
 
     # TODO: Set those parameters with existing or new config.yaml params.
     # Those parameters are set in the model, for isolated testing.