Doubly linked list with head/tail references for int values (Task 1)
and a generic LinkedList<T>/ListNode<T> version (Task 2). Both
implement add, get, remove, getSize with O(n/2) walks via the
closer-end heuristic. Includes IntLinkedListTest covering empty,
single-element, head/tail/middle removal, and out-of-bounds cases.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>