Type check the contents of untyped functions.

By default mypy doesn't type check the code within an untyped function.
This enables that and fixes typing errors to accomodate it.

This did uncover a very old bug:
https://github.com/dcs-liberation/dcs_liberation/issues/1417

(cherry picked from commit fc32b98341)

gen/groundobjectsgen.py

@@ -637,6 +637,7 @@ class GroundObjectsGenerator:
             ).generate()
 
             for ground_object in cp.ground_objects:
+                generator: GenericGroundObjectGenerator
                 if isinstance(ground_object, FactoryGroundObject):
                     generator = FactoryGenerator(
                         ground_object, country, self.game, self.m, self.unit_map