Add Stack implementation using Linked List

[praphull-verma]

Description

The current /stacks directory in the repository includes various stack algorithms and implementations
(e.g., using two queues, min stacks, postfix/prefix evaluation, etc.), but it lacks an implementation
of a Stack data structure using a Linked List.

Proposed Solution

Implemented a StackUsingLinkedList.java class under /stacks package that supports the following
standard stack operations:

• push(T data) – insert an element onto the stack
• pop() – remove and return the top element
• peek() – view the top element without removing it
• isEmpty() – check if the stack is empty
• size() – return the number of elements in the stack

Implementation Details

• Uses a singly linked list (with an inner Node class) to store elements.

• Ensures O(1) time complexity for push and pop operations.

• Includes proper exception handling and documentation comments.

• Added a simple main() method for demonstration and testing.

• I have read CONTRIBUTING.md.

• This pull request is all my own work -- I have not plagiarized it.

• All filenames are in PascalCase.

• All functions and variable names follow Java naming conventions.

• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.

• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.32%. Comparing base (b1aa896) to head (72c1467).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
...com/thealgorithms/stacks/StackUsingLinkedList.java	0.00%	34 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6717      +/-   ##
============================================
- Coverage     76.45%   76.32%   -0.14%     
- Complexity     5985     5986       +1     
============================================
  Files           716      717       +1     
  Lines         20265    20299      +34     
  Branches       3929     3930       +1     
============================================
- Hits          15494    15493       -1     
- Misses         4180     4215      +35     
  Partials        591      591              

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