Draw rat normally at tunnel entrances

Rats are now drawn fully (single animation frame) regardless of whether
they are on an open cell, a tunnel entrance, or an internal tunnel
passage. The only case where the rat is not drawn is when its center is
inside a wall (non-empty, non-tunnel cell).

Removed the now-unused _get_tunnel_entrance_direction helper.

units/rat.py

@@ -193,43 +193,16 @@ class Rat(Unit):
         cell_y = center_y // self.game.cell_size
 
         if self.game.map.in_bounds(cell_x, cell_y):
-            if self.game.map.is_tunnel(cell_x, cell_y):
+            if not self.game.map.is_tunnel(cell_x, cell_y) and not self.game.map.is_empty(cell_x, cell_y):
-                if self._get_tunnel_entrance_direction(cell_x, cell_y) is not None:
+                # Inside a wall (or otherwise non-visible cell): don't draw the rat.
-                    # Single entrance/exit: the rat is entering/leaving the tunnel.
-                    # Don't draw it; it disappears into the tunnel.
-                    return
-                # Internal tunnel passage or crossroad: draw the rat normally
-                # so it stays visible while walking through the tunnel.
-                frame = min(3, int(self.partial_move * 4))
-                source_rect = (frame * image_size[0], 0, image_size[0], image_size[1])
-                self.game.render_engine.draw_image(self.render_x, self.render_y, image, anchor="nw", tag="unit", source_rect=source_rect)
-                return
-            if not self.game.map.is_empty(cell_x, cell_y):
                 return
 
+        # Draw the rat (single animation frame). Applies to open cells, tunnel
+        # entrances, and internal tunnel passages alike.
         frame = min(3, int(self.partial_move * 4))
         source_rect = (frame * image_size[0], 0, image_size[0], image_size[1])
         self.game.render_engine.draw_image(self.render_x, self.render_y, image, anchor="nw", tag="unit", source_rect=source_rect)
 
-    def _get_tunnel_entrance_direction(self, cell_x, cell_y):
-        directions = [
-            ("UP", 0, -1),
-            ("DOWN", 0, 1),
-            ("LEFT", -1, 0),
-            ("RIGHT", 1, 0),
-        ]
-
-        empty_neighbors = []
-        for direction, dx, dy in directions:
-            neighbor_x = cell_x + dx
-            neighbor_y = cell_y + dy
-            if self.game.map.in_bounds(neighbor_x, neighbor_y) and self.game.map.is_empty(neighbor_x, neighbor_y):
-                empty_neighbors.append(direction)
-
-        if len(empty_neighbors) != 1:
-            return None
-        return empty_neighbors[0]
-
     def _calculate_render_position(self):
         """Calculate render position and bbox (used when render_x not yet set)"""
         sex = self.sex if self.age > AGE_THRESHOLD else "BABY"