Implemented nth Fibonacci number using different methods

[Gyan172004]

This PR introduces enhancements to the Fibonacci sequence calculation in the "Fibonacci.lua" file. It provides implementations for calculating the nth Fibonacci number using four different approaches with varying time complexities:

1. O(2^N): fibonacci_recursive(n) - Recursive approach.
2. O(N): fibonacci_dp(n) - Dynamic programming approach.
3. O(logN): fibonacci_matrix(n) - Matrix exponentiation approach.
4. O(1): fibonacci_binet(n) - Binet's formula approach.

Details

• Added comments and explanations for each function.
• Included assert tests for all four methods to ensure correctness.
• Reordered the functions from worst to best time complexity for clarity.

Please review and merge this PR to enhance the Fibonacci calculations in codebase.

Thank you!