1. Stack (Array-based)

Goal: Implement a stack using a dynamic array to handle elements in a Last In First Out (LIFO) manner.

🔧 Implementation Tasks:

• [x] Create StackArray class with internal resizable array
• [x] Implement push(value) — add element to end
• [x] Implement pop() — remove element from end
• [x] Implement peek() — return last element without removing
• [x] Implement getSize() — current number of elements
• [x] Implement isEmpty() — check if stack is empty

🧪 Test Tasks:

• [x] Initialize an empty stack
• [x] Push elements to the stack
• [x] Pop elements from the stack
• [x] Peek on non-empty stack
• [x] Return undefined when popping empty stack
• [x] Return undefined when peeking empty stack

2. Stack (LinkedList-based)

Goal: Implement a stack using a singly linked list for LIFO behavior.