Improve fibonacci caching

Author: AliQassab

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,4 +1,13 @@
+cache = {}
+
 def fibonacci(n):
+    if n in cache:
+        return cache[n]
+    
     if n <= 1:
-        return n
-    return fibonacci(n - 1) + fibonacci(n - 2)
+        result = n
+    else:
+        result = fibonacci(n - 1) + fibonacci(n - 2)
+    
+    cache[n] = result
+    return result