Fibonacci Function

Overview:
The Fibonacci function calculates the nth number in the Fibonacci sequence.
The sequence is defined as:
fibonacci(0) = 0
fibonacci(1) = 1
fibonacci(n) = fibonacci(n-1) + fibonacci(n-2) for n > 1

Implementation Details:

Basic Recursive Approach:  
    Utilizes a simple recursive method to compute the Fibonacci number.  
    Suitable for small values of n.  

Optimized Approach with Memoization:  
    Incorporates memoization to store and reuse previously computed values.  
    Reduces redundant calculations and improves performance, making it efficient for 
    larger values of n.  

Complexity:

Basic Recursive:  
    Exponential time complexity O(2^n).  

Memoized:  
    Linear time complexity O(n), with additional space complexity for storing results.  

Examples:
fibonacci(0) returns 0
fibonacci(1) returns 1
fibonacci(5) returns 5
fibonacci(10) returns 55

Usage:
The basic recursive implementation is best suited for educational purposes or small inputs.
The memoized implementation is recommended for applications requiring efficient computation of large Fibonacci numbers.