feat: implement cache on fibonacci

Author: JanefrancessC

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,4 +1,12 @@
+_cache = {}
+
 def fibonacci(n):
+    if n in _cache:
+        return _cache[n]
+    
     if n <= 1:
         return n
-    return fibonacci(n - 1) + fibonacci(n - 2)
+    
+    result = fibonacci(n - 1) + fibonacci(n - 2)
+    _cache[n] = result
+    return result