feat: add problem (217. Contains Duplicate) with unit testing

[mathusanm6]

closes #69

[Copilot]

Pull Request Overview

This PR adds a complete implementation of LeetCode problem 217 "Contains Duplicate" with solutions in both Python and C++, comprehensive unit tests, and documentation updates.

• Implements the contains duplicate algorithm using hash sets for O(n) time complexity
• Adds comprehensive test suites for both Python and C++ implementations covering edge cases and performance scenarios
• Updates repository documentation to reflect the new problem addition

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
problems/contains_duplicate/contains_duplicate.py	Python implementation using set for duplicate detection
problems/contains_duplicate/contains_duplicate.cc	C++ implementation using unordered_set with performance optimizations
problems/contains_duplicate/contains_duplicate.h	Header file declaring the C++ function signature
problems/contains_duplicate/contains_duplicate_test.py	Comprehensive Python test suite with parametrized test cases
problems/contains_duplicate/contains_duplicate_test.cc	C++ test suite using Google Test framework
problems/contains_duplicate/config.yml	Problem configuration metadata
README.md	Updated solution count badges and problem table entry

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