v1.1: Performance optimizations and bug fixes

Major improvements:
- NumPy-based collision system supporting 200+ units (~3ms/frame)
- Spatial hashing with vectorized distance calculations
- 4-pass game loop ensuring correct collision timing
- Blood overlay system with pre-generated stain pool
- Cached render positions and viewport bounds
- Spawn protection preventing rats spawning on weapons

Bug fixes:
- Fixed bombs not killing rats (collision system timing)
- Fixed gas not affecting rats (collision system timing)
- Fixed rats spawning on weapons (added has_weapon_at check)
- Fixed AttributeError with Gas collisions (added isinstance check)
- Fixed blood stain transparency (RGBA + SDL_BLENDMODE_BLEND)
- Reduced point lifetime from 200 to 90 frames (~1.5s)
- Blood layer now clears on game restart

Technical changes:
- Added engine/collision_system.py with CollisionLayer enum
- Updated all units to use collision layers
- Pre-allocate NumPy arrays with capacity management
- Hybrid collision approach (<10 simple, ≥10 vectorized)
- Python 3.13 compatibility

user_profiles.json

@@ -3,7 +3,7 @@
     "Player1": {
       "name": "Player1",
       "created_date": "2024-01-15T10:30:00",
-      "last_played": "2025-10-24T19:07:22.052062",
+      "last_played": "2025-10-24T19:57:33.897466",
       "games_played": 25,
       "total_score": 15420,
       "best_score": 980,