Support polygons with holes in the API.

We don't have any of these yet because our landmaps suck, but we'll need
holes in the sea zones to mask islands correctly.

game/server/leaflet.py

@@ -20,7 +20,15 @@ class LeafletPoint(BaseModel):
         title = "LatLng"
 
 
-LeafletPoly = list[LeafletPoint]
+LeafletLine = list[LeafletPoint]
+
+
+# Leaflet allows either a single array of latlng to define the boundary, or an array of
+# arrays of latlngs, with the first array being the boundary and the rest defining
+# holes. To avoid the UI needing to test for which type of polygon we send, we always
+# use the array of arrays type, even for geometries without holes.
+# https://leafletjs.com/reference.html#polygon
+LeafletPoly = list[LeafletLine]
 
 
 class ShapelyUtil:
@@ -32,10 +40,11 @@ class ShapelyUtil:
     def poly_to_leaflet(cls, poly: Polygon, theater: ConflictTheater) -> LeafletPoly:
         if poly.is_empty:
             return []
-        return [
-            cls.latlng_to_leaflet(Point(x, y, theater.terrain).latlng())
-            for x, y in poly.exterior.coords
-        ]
+        try:
+            lines = poly.boundary.geoms
+        except AttributeError:
+            lines = [poly.boundary]
+        return cls.lines_to_leaflet(MultiLineString(lines), theater)
 
     @classmethod
     def polys_to_leaflet(
@@ -47,14 +56,17 @@ class ShapelyUtil:
             polys = [poly]
         return [cls.poly_to_leaflet(poly, theater) for poly in polys]
 
-    @staticmethod
-    def line_to_leaflet(line: LineString, theater: ConflictTheater) -> list[LatLng]:
-        return [Point(x, y, theater.terrain).latlng() for x, y in line.coords]
+    @classmethod
+    def line_to_leaflet(cls, line: LineString, theater: ConflictTheater) -> LeafletLine:
+        return [
+            cls.latlng_to_leaflet(Point(x, y, theater.terrain).latlng())
+            for x, y in line.coords
+        ]
 
     @classmethod
     def lines_to_leaflet(
         cls, line_string: MultiLineString | LineString, theater: ConflictTheater
-    ) -> list[list[LatLng]]:
+    ) -> list[LeafletLine]:
         if isinstance(line_string, MultiLineString):
             lines = line_string.geoms
         else: