Constrain front lines better.

Holes in the inclusion zone are defined by exclusion zones, not by holes
in the inclusion zone. Add a cached property for the inclusion zone that
is not also sea or exclusion zone and use that boundary instead.

game/theater/landmap.py

@@ -1,5 +1,6 @@
 from dataclasses import dataclass
 import pickle
+from functools import cached_property
 from typing import Optional, Tuple, Union
 import logging
 
@@ -13,6 +14,18 @@ class Landmap:
     exclusion_zones: MultiPolygon
     sea_zones: MultiPolygon
 
+    def __post_init__(self):
+        if not self.inclusion_zones.is_valid:
+            raise RuntimeError("Inclusion zones not valid")
+        if not self.exclusion_zones.is_valid:
+            raise RuntimeError("Exclusion zones not valid")
+        if not self.sea_zones.is_valid:
+            raise RuntimeError("Sea zones not valid")
+
+    @cached_property
+    def inclusion_zone_only(self) -> MultiPolygon:
+        return self.inclusion_zones - self.exclusion_zones - self.sea_zones
+
 
 def load_landmap(filename: str) -> Optional[Landmap]:
     try: