Add hidden duck types: Normal, Golden, and Fast ducks

Features:
- Three duck types spawn randomly with configurable chances
- All duck types use same spawn message - type is hidden until shot/timeout
- Golden ducks: 3-5 HP, 15 XP base, reveal type when hit but still alive
- Fast ducks: 1 HP, 12 XP, fly away in 30s instead of 60s
- Normal ducks: 1 HP, 10 XP, standard 60s timeout

Configuration options:
- golden_duck_chance: 0.15 (15% spawn rate)
- fast_duck_chance: 0.25 (25% spawn rate)
- golden_duck_xp: 15, golden_duck_min/max_hp: 3-5
- fast_duck_xp: 12, fast_duck_timeout: 30s

Duck type is revealed when:
- Shot (different messages for each type)
- Flies away (type-specific fly away messages)
- Golden ducks reveal immediately when hit (before death)

Maintains backward compatibility with existing game mechanics.

config.json

@@ -16,6 +16,15 @@
     "duck_spawn_max": 30,
     "duck_timeout": 60,
     "befriend_success_rate": 75,
-    "rearm_on_duck_shot": true
+    "rearm_on_duck_shot": true,
+    
+    "golden_duck_chance": 0.15,
+    "golden_duck_min_hp": 3,
+    "golden_duck_max_hp": 5,
+    "golden_duck_xp": 15,
+    
+    "fast_duck_chance": 0.25,
+    "fast_duck_timeout": 30,
+    "fast_duck_xp": 12
     
 }