Core: Only error in playthrough generation if game is not beatable

The current flow of accessibility works like this:

```
if fulfills_accessibility fails:
    if multiworld can be beaten:
        log a warning
    else:
        raise Exception

if playthrough is enabled:
    if any progression items are not reachable:
        raise Exception
```

This means that if you do a generation where the game is beatable but some full players' items are not reachable, it doesn't crash on accessibility check, but then crashes on playthrough. This means that **whether it crashes depends on whether you have playthrough enabled or not**.

Imo, erroring on something accessibility-related is outside of the scope of create_playthrough. Create_playthrough only needs to care about whether it can fulfill its own goal - Building a minimal playthrough to everyone's victory.
The actual accessibility check should take care of the accessibility.

BaseClasses.py

@@ -1719,9 +1719,9 @@ class Spoiler:
                 logging.debug('The following items could not be reached: %s', ['%s (Player %d) at %s (Player %d)' % (
                     location.item.name, location.item.player, location.name, location.player) for location in
                                                                                sphere_candidates])
-                if any([multiworld.worlds[location.item.player].options.accessibility != 'minimal' for location in sphere_candidates]):
-                    raise RuntimeError(f'Not all progression items reachable ({sphere_candidates}). '
-                                       f'Something went terribly wrong here.')
+                if not multiworld.has_beaten_game(state):
+                    raise RuntimeError(f'Not all progression items reachable ({sphere_candidates}), and as a result, '
+                                       f'the multiworld was not beatable. Something went terribly wrong here.')
                 else:
                     self.unreachables = sphere_candidates
                     break