Bridge tear test without imps (they would mend the bridge)

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

src/game.rs

@@ -6018,6 +6018,8 @@ mod tests {
         }
         g.map.t[idx(bx, by)].kind = Kind::Bridge;
         g.map.t[idx(bx, by)].owner = Owner::Player;
+        // no imps around to mend it (and to be attacked instead)
+        g.ents.retain(|e| e.hero);
         let mut torn = false;
         for _ in 0..(90 * 20) {
             g.update(0.05);