docs, test: fit edit_distance.cpp to contributing guidelines

[rahulpaul-07]

Description of Change

This PR updates dynamic_programming/edit_distance.cpp to align with the modern contribution guidelines and significantly improves the algorithm's efficiency.

Changes:

• Space Optimization: Refactored the core logic from O(m * n) to O(n) space complexity using a two-row dynamic programming approach.
• Namespace Encapsulation: Wrapped the implementation in the dynamic_programming namespace to prevent global scope pollution.
• Doxygen Documentation: Added full Doxygen-style headers for the file and functions, including Wikipedia references and parameter descriptions.
• Security Gating: Added a defensive check to prevent memory exhaustion (DoS) for inputs exceeding 10,000 characters.
• Automated Testing: Replaced interactive std::cin inputs with a comprehensive suite of automated assert tests covering edge cases (empty strings, identical strings, and case sensitivity).
• Code Quality: Cleaned up headers, removed using namespace std;, and ensured strict type safety with static_cast.

Related Issue:

Fixes #2456