Implement optimized collision detection system using NumPy

- Introduced a hybrid collision detection approach that utilizes NumPy for vectorized operations, improving performance for games with many entities (200+).
- Added a spatial grid for efficient lookups and AABB (Axis-Aligned Bounding Box) collision detection.
- Implemented a new `CollisionSystem` class with methods for registering units, checking collisions, and managing spatial data.
- Created performance tests to benchmark the new collision system against the old O(n²) method, demonstrating significant speed improvements.
- Updated existing code to integrate the new collision detection system and ensure compatibility with game logic.

units/mine.py

@@ -1,8 +1,10 @@
 from .unit import Unit
 from .bomb import Explosion
+from engine.collision_system import CollisionLayer
+
 class Mine(Unit):
     def __init__(self, game, position=(0,0), id=None):
-        super().__init__(game, position, id)
+        super().__init__(game, position, id, collision_layer=CollisionLayer.MINE)
         self.speed = 1.0  # Mine doesn't move but needs speed for consistency
         self.armed = True  # Mine is active and ready to explode
 
@@ -11,13 +13,18 @@ class Mine(Unit):
         pass
         
     def collisions(self):
-        """Check if a rat steps on the mine (has position_before on mine's position)."""
+        """Check if a rat steps on the mine using optimized collision system."""
         if not self.armed:
             return
-            
-        # Check for rats that have position_before on this mine's position
-        for rat_unit in self.game.unit_positions_before.get(self.position, []):
-            if hasattr(rat_unit, 'sex'):  # Check if it's a rat (rats have sex attribute)
+        
+        # Use collision system to check for rats at mine's position_before
+        victim_ids = self.game.collision_system.get_units_in_cell(
+            self.position, use_before=True
+        )
+        
+        for victim_id in victim_ids:
+            rat_unit = self.game.get_unit_by_id(victim_id)
+            if rat_unit and hasattr(rat_unit, 'sex'):  # Check if it's a rat
                 # Mine explodes and kills the rat
                 self.explode(rat_unit)
                 break