feat: add Valid Parentheses algorithm using Stack

[Gokul45-45]

Description

This PR adds the Valid Parentheses algorithm implementation using Stack data structure.

Problem

Checks if a string containing parentheses (), brackets [], and braces {} is valid according to:

• Open brackets must be closed by the same type
• Open brackets must be closed in the correct order

Changes Made

• Added ValidParentheses.java in stacks package
• Added comprehensive unit tests in ValidParenthesesTest.java
• Includes edge case handling (null, odd length, empty string)

Testing

• All tests pass locally
• Covers valid cases: (), ()[]{}, {[]}
• Covers invalid cases: (], ([)], {{{

Closes #6724

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.50%. Comparing base (e841d73) to head (335732e).

Files with missing lines	Patch %	Lines
...ava/com/thealgorithms/stacks/ValidParentheses.java	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7117      +/-   ##
============================================
- Coverage     78.50%   78.50%   -0.01%     
- Complexity     6752     6757       +5     
============================================
  Files           759      760       +1     
  Lines         22402    22418      +16     
  Branches       4400     4404       +4     
============================================
+ Hits          17587    17599      +12     
- Misses         4109     4111       +2     
- Partials        706      708       +2     

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[Gokul45-45]

@DenizAltunkapan
could u please check and review the changes ,i would appereciate a quick response
,thank you!!