Add Middle of Linked List (Slow/Fast Pointers) (#7212)

* feat: implement Smooth Sort algorithm with detailed JavaDoc and test class

* style: format LEONARDO array for improved readability with clang-format

* feat: add MiddleOfLinkedList class and corresponding test cases

* docs: update documentation for MiddleOfLinkedList class

* test: refactor MiddleOfLinkedListTest to improve readability and assertions

* test: refactor MiddleOfLinkedListTest for improved null safety and readability

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Co-authored-by: Ahmed Allam <60698204+AllamF5J@users.noreply.github.com>