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 78.51%. Comparing base (f693c44) to head (7a68d2e).
⚠️ Report is 1 commits behind head on master.

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%   78.51%           
- Complexity     6752     6758    +6     
=========================================
  Files           759      760    +1     
  Lines         22402    22418   +16     
  Branches       4400     4404    +4     
=========================================
+ Hits          17587    17601   +14     
- Misses         4109     4110    +1     
- Partials        706      707    +1     

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[Gokul45-45]

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