Free game against rival dungeon masters (green, blue) and/or the humans

- One opponent on maps up to 128x128, two on bigger maps; with a chance of one in two one of
  them is the humans' gate instead of a rival master
- Simplified rival masters (rival.rs): own soul core and dungeon (lair, treasury to loot) that
  grows ring by ring, creatures appear and get stronger over time, guard the dungeon and attack
  in groups - the player, the other master or the humans' gate; a fallen core puts the master
  out and frees its ground
- The humans attack everybody: waves now and then march on a rival master
- Sides for units: all other sides are enemies; towers and contested ground follow them; the
  hand cannot pick up rival creatures; the flag next to a rival core attacks it
- Difficulty (easy / medium / hard) in the New Game dialog
- Colours: green and blue floors, cores, unit rings, minimap, HUD bars of the rival cores
- Victory in free games: every rival core and the gate (if any) destroyed
- Tests for setups, growth and attacks, elimination and victory, humans against rivals

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/map.rs

@@ -125,9 +125,23 @@ pub enum Owner {
     None,
     Player,
     Hero,
+    Rival1, // AI dungeon masters (free play, campaign)
+    Rival2,
 }
 
-const OWNERS: [Owner; 3] = [Owner::None, Owner::Player, Owner::Hero];
+const OWNERS: [Owner; 5] = [Owner::None, Owner::Player, Owner::Hero, Owner::Rival1, Owner::Rival2];
+
+impl Owner {
+    pub fn of_side(side: u8) -> Owner {
+        match side {
+            0 => Owner::Player,
+            1 => Owner::Hero,
+            2 => Owner::Rival1,
+            3 => Owner::Rival2,
+            _ => Owner::None,
+        }
+    }
+}
 
 // Short serde names (only used by version 1 savegames, newer ones use the packed codec)
 #[derive(Clone, Copy, PartialEq, Serialize, Deserialize)]
@@ -648,15 +662,22 @@ impl Map {
         }
     }
 
+    // next to the player's soul core
     pub fn adj_core(&self, i: usize) -> bool {
+        self.adj_core_of(i, Owner::Player)
+    }
+
+    // next to the soul core of a master (player or rival)
+    pub fn adj_core_of(&self, i: usize, owner: Owner) -> bool {
         let (x, y) = xy(i);
-        DIR4.iter().any(|&(dx, dy)| self.get(x + dx, y + dy).map_or(false, |t| t.kind == Kind::Core))
+        DIR4.iter().any(|&(dx, dy)| self.get(x + dx, y + dy).map_or(false, |t| t.kind == Kind::Core && t.owner == owner))
     }
 
     pub fn hero_path_to_core(&self, start: usize) -> Option<Vec<usize>> {
         self.search(start, self.hero_cost(), |i| self.adj_core(i), true)
     }
 
+
     pub fn path_to(&self, start: usize, target: usize) -> Option<Vec<usize>> {
         self.search(start, self.walk_cost(), |i| i == target, true)
     }