Add Solution for Largest element in an array

[sriram1302]

This pull request introduces a Python solution to find the largest element in an input array. The modifications are:

• Added the function largest_element(arr), which returns the maximum value from the input list.
• Created an equivalent test function test_largest_element() that verifies the correctness of the implementation through a common test case.
• Applied the Test-Driven Development (TDD) procedure by initially creating a failing test, subsequently coming up with the functional code to pass the test, and finally refactoring the code for readability and maintainability.

This submission meets the requirements outlined in Issue #7 with a simple, tried-and-tested solution that can be integrated within the repository.