[akhila-pynam]

Summary of Changes

• Implements the Sliding Window Maximum algorithm using a monotonic double-ended queue (std::deque) in data_structures/sliding_window_maximum.cpp.
• Time Complexity: $\mathcal{O}(N)$ as each element index is pushed and popped from the deque at most once.
• Auxiliary Space Complexity: $\mathcal{O}(k)$ for storing up to $k$ indices.
• Supports generic numeric types (template <typename T>) with handling for edge cases (empty, k == 0, k >= N).
• Includes a comprehensive self-test suite using assert().
• Formatted with clang-format and complies with clang-tidy rules.

Fixes #3225