feat(cpp): add valid palindrome

[mathusanm6]

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[Copilot]

Pull Request Overview

This PR adds a C++ implementation of the "Valid Palindrome" algorithm that checks if a string is a palindrome when considering only alphanumeric characters and ignoring case. The implementation uses a two-pointer approach for efficient character comparison.

Key changes:

• Implements the core palindrome validation algorithm with alphanumeric filtering and case-insensitive comparison
• Adds comprehensive test coverage with 26 test cases covering edge cases and various input patterns
• Updates CI workflow to optimize build performance and add better change detection

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
problems/valid_palindrome/valid_palindrome.cc	Core implementation using two-pointer technique with string transformation
problems/valid_palindrome/valid_palindrome.h	Function declaration for the palindrome checker
problems/valid_palindrome/valid_palindrome_test.cc	Comprehensive test suite with parameterized tests
Makefile	Minor test execution improvements
.github/workflows/cpp-package.yml	Enhanced CI workflow with change detection and performance optimizations

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