Add Bellman-Ford shortest path algorithm

[DeadJoker24]

Description of Change

This PR adds an implementation of the Bellman-Ford shortest path algorithm.

The implementation:

• Computes shortest paths from a single source vertex.
• Supports graphs with negative edge weights.
• Detects negative-weight cycles.
• Includes multiple test cases using assert.
• Follows the project's coding style and documentation format.

The implementation has been compiled and all included test cases pass successfully.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:
Adds an implementation of the Bellman-Ford shortest path algorithm with negative cycle detection.