[28/N] Add unit tests for BST, AVL, Heap, and SplayTree algorithms

[karkir0003]

🥞 Stack

1. ⬅️ [1/N] Update CI to run frontend unit tests #91 (Add test infrastructure and Jest setup)
2. ⬅️ [2/N] Configure React Testing Library and Setup Tests #92 (Add unit tests for Footer, Header, and Blob components)
3. ⬅️ [3/N] Add unit tests for SideButton component #94 (Add unit tests for AlgorithmNotFound404 component)
4. ⬅️ [4/N] Add unit tests for SearchFilter component #95 (Add unit tests for Pseudocode component)
5. ⬅️ [5/N] Add unit tests for Header and Footer components #96 (Add unit tests for AlgoSection component)
6. ⬅️ [6/N] Add unit tests for Blob mascot component #97 (Add unit tests for ModalSidebarSectionTab component)
7. ⬅️ [7/N] Add unit tests for AboutScreen screen #98 (Add unit tests for BigOModal component)
8. ⬅️ [8/N] Add integration tests for HomeScreen screen #99 (Add unit tests for InfoModals component)
9. ⬅️ [9/N] Add unit tests for AlgorithmNotFound404 component #100 (Add unit tests for SideButton component)
10. ⬅️ [10/N] Add integration tests for AlgoScreen screen #101 (Add unit tests for SearchFilter component)
11. ⬅️ [11/N] Add unit tests for ModalSidebarSectionTab component #102 (Add unit tests for HomeScreen)
12. ⬅️ [12/N] Add unit tests for BigOModal component #103 (Add unit tests for AboutScreen)
13. ⬅️ [13/N] Add unit tests for Pseudocode component #104 (Add unit tests for AlgoScreen)
14. ⬅️ [14/N] Add unit and integration tests for AlgoSection component #105 (Add unit tests for AlgoList registry)
15. ⬅️ [15/N] Add unit and integration tests for root App component #106 (Add unit and integration tests for root App component)
16. ⬅️ [16/N] Add unit tests for animation events and undo functions #107 (Add unit tests for animation events and undo functions)
17. ⬅️ [17/N] Add unit tests for AnimatedObject, AnimatedCircle, and AnimatedHighlightCircle #108 (Add unit tests for AnimatedObject, AnimatedCircle, and AnimatedHighlightCircle)
18. ⬅️ [18/N] Add unit tests for AnimatedRectangle, AnimatedLabel, and AnimatedLine #109 (Add unit tests for AnimatedRectangle, AnimatedLabel, and AnimatedLine)
19. ⬅️ [19/N] Add unit tests for AnimatedLinkedListNode, AnimatedDoublyLinkedListNode, and AnimatedCircularlyLinkedListNode #110 (Add unit tests for AnimatedLinkedListNode, AnimatedDoublyLinkedListNode, and AnimatedCircularlyLinkedListNode)
20. ⬅️ [20/N] Add unit tests for AnimatedBTreeNode and AnimatedSkipListNode #111 (Add unit tests for AnimatedBTreeNode and AnimatedSkipListNode)
21. ⬅️ [21/N] Add unit tests for ObjectManager #112 (Add unit tests for ObjectManager)
22. ⬅️ [22/N] Add unit tests for AnimationMain #113 (Add unit tests for AnimationMain)
23. ⬅️ [23/N] Add unit tests for algo util helpers (PriorityQueue, SkipListHeads, GraphValues) #114 (Add unit tests for algo util helpers (PriorityQueue, SkipListHeads, GraphValues))
24. ⬅️ [24/N] Add unit tests for base Algorithm class and control bar helpers #115 (Add unit tests for base Algorithm class and control bar helpers)
25. ⬅️ [25/N] Add unit tests for ArrayList algorithm #116 (Add unit tests for ArrayList algorithm)
26. ⬅️ [26/N] Add unit tests for LinkedList, DoublyLinkedList, and CircularlyLinkedList algorithms #117 (Add unit tests for LinkedList, DoublyLinkedList, and CircularlyLinkedList algorithms)
27. ⬅️ [27/N] Add unit tests for Stack, Queue, and Deque algorithms (Array and LL variants) #118 (Add unit tests for Stack, Queue, and Deque algorithms (Array and LL variants))
28. 👉 #CURRENT — Add unit tests for BST, AVL, Heap, and SplayTree algorithms (this PR)
29. ➡️ [29/N] Add unit tests for BTree, TreeMap, SkipList, and DisjointSet algorithms #120 (Add unit tests for BTree, TreeMap, SkipList, and DisjointSet algorithms)

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Addresses #93

Context

Adds comprehensive unit test coverage for the core tree and heap visualizer algorithms:

• BST.js: Binary Search Tree with recursive insertions, find, successor deletions (leaf, one child, two children), traversals (preorder, inorder, postorder), and resize/reposition logic.
• AVL.js: Self-balancing binary search tree with height updates, balance factors, single (left, right) and double (left-right, right-left) rotations.
• Heap.js: Min/max binary heap with array visualizer, insert with bubble-up, remove root with trickle-down, and buildHeap (bottom-up Floyd's algorithm).
• SplayTree.js: Self-adjusting binary search tree with splaying operations (zig, zig-zig, zig-zag) on insert, find, and delete.

Changes Made

• Introduced src/algo/__tests__/BST.test.js:
  • Control registration (insert, delete, find, print, clear).
  • Insertion (root, left/right branching, duplicates).
  • Search/find (hit and miss).
  • Deletion cases: leaf node, single-child node, two-child node with successor replacement.
  • Traversals: preorder, inorder, postorder callback flows.
  • URL data hydration (setURLData) and clear operations.
• Introduced src/algo/__tests__/AVL.test.js:
  • AVL tree node properties (height, balance factor).
  • Rotations: Right rotation (LL case), Left rotation (RR case), Left-Right rotation (LR case), Right-Left rotation (RL case).
  • Insertions and deletions triggering cascading rebalancing.
  • Traversals, search, empty tree edge cases, and URL parameter deserialization.
• Introduced src/algo/__tests__/Heap.test.js:
  • Min-heap operations: insert with percolate/bubble up, extract min with trickle-down.
  • Max-heap operations: insert and extract max with child comparisons.
  • Bottom-up heapify (buildHeap from arbitrary values).
  • Array representation synchronization with tree node positions.
  • Boundary cases (empty heap removal, random fill, capacity limits).
• Introduced src/algo/__tests__/SplayTree.test.js:
  • Splay operations: Zig (root child), Zig-Zig (same side), Zig-Zag (opposite side).
  • Splay on insert (inserted element splayed to root).
  • Splay on find (found element splayed to root, or last accessed node on miss).
  • Deletion with splaying and subtree joining.
  • Traversals, reset, clear, and URL data loading.

Test Plan

• Ran npm test -- --watchAll=false (all 4 new test suites pass, 64 unit tests passing).
• Ran npm run lint and npm run prettier (0 errors, 0 warnings).