feat: Add Depth-First Search (DFS)

[monkey0722]

This pull request introduces a new Depth-First Search (DFS) implementation for graphs, including both the core DFS functionality and comprehensive unit tests to validate the implementation. The main changes are the addition of the DFS class, which supports various DFS operations, and the corresponding test cases to ensure correctness.

DFS Implementation:

• src/graph/dfs.hpp: Added a new DFS class template that supports various DFS operations including traversal, recursive traversal, path finding, cycle detection, topological sort, and counting connected components.

Unit Tests:

• tests/graph/dfs_test.cpp: Added unit tests for the DFS class to validate basic traversal, recursive traversal, path finding, cycle detection, topological sort, counting connected components, and custom node types.…hfinding, cycle detection, and topological sorting