Add compute_z_array Function with Unit Tests

[Simranstha045]

PR Description:

This PR introduces the implementation of the compute_z_array function, which computes the Z-array for a given string in linear time, as well as comprehensive unit tests to verify its correctness.

Description of compute_z_array Function:

The compute_z_array function calculates the Z-array for a string, where each element at index i represents the length of the longest substring starting from index i that is also a prefix of the string.

Key Features:

• Utilizes the Z-box technique to reduce unnecessary comparisons.
• Processes the string in linear time.

Use case:
The Z Algorithm is like a super-smart search tool that looks at parts of a string and tells you how much they match the beginning of the string. It's useful when you want to find patterns quickly, like searching for words in a long text, detecting DNA sequences, or even finding virus patterns in files. It does all this in a smart way, skipping unnecessary checks, so it's super fast!

Unit Tests for compute_z_array:

The following tests have been added to ensure robustness:

• Basic Test Cases: Verifies correct Z-array generation for strings with repeating patterns (e.g., "aaaaa" and "ababa").
• Edge Case Tests:
  • Strings with no prefix matches (e.g., "abcde").
  • Full match strings (e.g., "aaaa").
  • Mixed case strings with partial matches.
  • Single character strings.
  • Empty string input.

These unit tests ensure the function works as expected across a range of inputs, providing confidence in its correctness and edge-case handling.

All tests have been added under the unittest framework to maintain consistency with the existing test suite.