Add cycle creation utility and detection tests for Linked List (Fixes #583)

[sowmya-rebbavarapu]

Description:
This pull request adds the ability to create a cycle in the linked list by linking the tail node to any node at a specified position. It includes:

A utility function createCycle(list, position) that links the last node to the node at the given position to form a cycle.

Unit tests to verify cycle creation and detection using the existing detectCycle function.

Tests cover normal cases, invalid positions, and no-cycle scenarios.

This addresses the feature request in issue #583 opened by @chrisVillanueva, enabling users to create and detect cycles within linked lists for more comprehensive linked list operations.

Please review the implementation and tests. Looking forward to your feedback!

[lazarljubenovic]

That's not a linked list anymore.

[Imran-imtiaz48]

Great job on this test suite! Here are some specific observations and suggestions:

Positives

• Test Coverage: The tests cover a good range of scenarios, including:
  • No cycle in the linked list
  • Correct cycle creation and detection
  • Handling invalid positions for cycle creation (out-of-bounds and negative)
• Readability: Test cases are clear and descriptive, making it easy to understand the intention behind each scenario.
• Setup: Using beforeEach to initialize a new LinkedList keeps tests isolated and reliable.

Suggestions/Improvements

1. Edge Cases:
   Consider adding tests for these edge cases:

   • An empty list (should return false for cycle detection).
   • A list with a single node (cycle vs. no cycle).
   • Creating a cycle at position 0 (head node).

2. Assertions:
   If createCycle returns a value (such as success/failure), consider asserting it as well to make the effect of the function explicit.

3. Comments:
   Your current comments are helpful! If possible, expand them a bit for maintainability, especially in less obvious scenarios.

4. Consistency:
   The pattern and naming are consistent and align with best practices for unit testing in JavaScript.

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