Fix bomb explosions not killing rats and remove tracked pycache

- Move Timer explosion from move() to collisions() so all units are
  registered in the collision system before the kill query runs.
- Explosion units now set a bbox and kill rats that touch them.
- Guard Rat.draw() so dead rats are not drawn.
- Remove units/__pycache__ files from tracking.

units/bomb.py

@@ -55,32 +55,31 @@ class Timer(Bomb):
 
     def move(self):
         self.age += self.speed
-        if self.age == AGE_THRESHOLD:
-            self.die()
+        if self.age >= AGE_THRESHOLD and not getattr(self, "exploded", False):
+            self.exploding = True
 
-    def die(self, unit=None, score=None):
-        """Handle bomb explosion and chain reactions using vectorized collision system."""
+    def collisions(self):
+        """Explode in Pass 2 when every unit is registered in the collision system."""
+        if getattr(self, "exploding", False) and not getattr(self, "exploded", False):
+            self.explode()
+
+    def explode(self):
+        """Handle bomb explosion and chain reactions."""
         score = 10
         print("BOOM")
-        target_unit = unit if unit else self
         self.game.render_engine.play_sound("BOMB.WAV")
+        self.exploded = True
 
-        # Use base class cleanup with error handling
-        try:
-            if target_unit.id in self.game.units:
-                self.game.units.pop(target_unit.id)
-        except:
-            print(f"Unit {target_unit.id} already dead")
+        # Remove bomb
+        if self.id in self.game.units:
+            self.game.units.pop(self.id)
 
-        # Bomb-specific behavior: create explosion
-        self.game.unit_manager.spawn_unit(Explosion, target_unit.position)
-
-        # Collect all explosion positions using vectorized approach
+        # Collect all explosion positions
         explosion_positions = []
 
         # Check for chain reactions in all four directions
         for direction in ["N", "S", "E", "W"]:
-            x, y = target_unit.position
+            x, y = self.position
             while True:
                 if not self.game.map.is_wall(x, y):
                     explosion_positions.append((x, y))
@@ -95,28 +94,30 @@ class Timer(Bomb):
                 elif direction == "W":
                     x -= 1
 
-        # Create all explosions at once
+        # Create visual explosions
         for pos in explosion_positions:
             self.game.unit_manager.spawn_unit(Explosion, pos)
 
-        # Use optimized collision system to get all rats in explosion area
-        # This replaces the nested loop with a single vectorized operation
+        # Kill all rats in explosion area (Pass 2: all units registered)
         victim_ids = self.game.collision_system.get_units_in_area(
-            explosion_positions, 
+            explosion_positions,
             layer_filter=CollisionLayer.RAT
         )
 
-        # Kill all victims with score multiplier
         for victim_id in victim_ids:
             victim = self.game.unit_manager.get_unit_by_id(victim_id)
             if victim and victim.id in self.game.units:
-                # Determine position based on partial_move
-                victim_pos = victim.position if victim.partial_move >= 0.5 else victim.position_before
-                if victim_pos in explosion_positions:
+                if victim.position in explosion_positions or victim.position_before in explosion_positions:
                     victim.die(score=score)
                     if score < 160:
                         score *= 2
 
+    def draw(self):
+        """Don't draw a bomb that has already exploded."""
+        if getattr(self, "exploded", False):
+            return
+        super().draw()
+
 
 class Explosion(Bomb):
     def __init__(self, game, position=(0,0), id=None):
@@ -129,6 +130,20 @@ class Explosion(Bomb):
         self.age += self.speed
         if self.age >= AGE_THRESHOLD:
             self.die()
+        # Set bbox so lingering explosions can kill rats via collision system
+        x = self.position[0] * self.game.cell_size
+        y = self.position[1] * self.game.cell_size
+        self.bbox = (float(x), float(y), float(x + self.game.cell_size), float(y + self.game.cell_size))
+
+    def collisions(self):
+        """Lingering explosion kills any rat that touches it."""
+        victim_ids = self.game.collision_system.get_collisions_for_unit(
+            self.id, CollisionLayer.EXPLOSION, tolerance=0
+        )
+        for _, victim_id in victim_ids:
+            victim = self.game.unit_manager.get_unit_by_id(victim_id)
+            if victim and victim.type in [UnitType.RAT_MALE, UnitType.RAT_FEMALE] and victim.id in self.game.units:
+                victim.die(score=10)
 
     def draw(self):
         image = self.game.graphics.assets["BMP_EXPLOSION"]

units/rat.py

@@ -171,6 +171,8 @@ class Rat(Unit):
 
     def draw(self):
         """Optimized draw using pre-calculated positions from move()"""
+        if self.id not in self.game.units:
+            return
         sex = self.sex if self.age > AGE_THRESHOLD else "BABY"
         image = self.game.graphics.rat_assets_textures[sex][self.direction]
         image_size = self.game.graphics.rat_image_sizes[sex][self.direction]